Minor Project Report (1)
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Transcript of Minor Project Report (1)
ABSTRACT
With the advances of technology, security of the digital media has become a major challenge.
One way to ensure safety and control over the unauthorized distribution of the media is to
effectively hide some classified information in it so that the intellectual property rights of the
owner can be proved as and when required.
Watermarking is the technique to embed some data into the signal for identifying the copyright
ownership and preventing piracy. By pre-processing the image watermark and hiding it in a
carrier stream, a robust watermarking technique is presented, resisting all the signal processing
manipulations and deliberate attacks. In digital watermarking, the signal may be audio, pictures,
or video. If the signal is copied, then the information also is carried in the copy. A signal may
carry several different watermarks at the same time.
Digital watermarking is a technology that opens a new door for authors, producers, publishers
and service providers for protection of their rights and interest in multimedia documents.
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CHAPTER 1
Introduction
With the rapid growth of Internet, it is easier for digital data owners to transit multimedia files
across the Internet. Thus, there is a huge increase in concentration overcopyright protection of
media. Traditionally, encryption and control access techniques were used to protect the
intellectual property rights. These techniques do not protect against unauthorized copying after
the media have been successfully transmitted and decrypted.
Cryptography guarantees confidentiality, authenticity, and integrity when a message is
transmitted across the network. It does not protect against unauthorized copying after
successful message transmission. Watermarking is an efficient way to protect copyright of
media. Watermarking is a technique of embedding a special pattern, watermark, into a
multimedia document so that a given piece of copyright information is permanently tied to the
data. This information can later prove the ownership, identify a misappropriating person, trace
the marked documents dissemination through the network, or simply inform users about the
rights-holder or the permitted use of the data.
Motivation
The technological advances have led to the multiple copying of digital media without incurring a
loss in quality. These unlimited copying causes a considerable loss to the copyright holders. To
enforce intellectual property rights and to restrain the unauthorized distribution of the media,
some information is hidden in it for proving the ownership. Hence, the main motivation for
taking watermarking as a research topic is to develop an effiective algorithm for embedding and
extraction of the hidden information (watermark) for data files. The goal in this project is to
embed the watermark in the audio signal imperceptibly by the exploitation of the statistical and
the objective properties of the cover signal. The low frequency region and the energy of the
signal segments are considered in this regard. Lastly, the robustness of the implemented strategy
is evaluated against signal processing and intentional attacks which mainly include the de-
synchronization attacks and this defines the final aim of the undertaken project.
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1.1 Objective
1. To develop an effective algorithm for embedding and extraction of the hidden information
(watermark) for files.
2. To embed watermark imperceptibly by exploiting the statistical and the objective properties.
3. To evaluate robustness of the implemented strategy against de-synchronization attacks.
1.2 Digital Watermarking
With the advancements in technology and increased access to the digital media, the copyright
protection of media has gained a lot of importance. To prevent piracy of media and its
unauthorized distribution, the owner or the creator of the media needs to prove his intellectual
property rights. This is where watermarking comes into picture. Watermarking is a strategy to
embed some classified information into the media perceptually or non-perceptually to prove the
ownership. Watermark is the data which is hidden into the digital media for proving the
intellectual property rights. The main properties of the watermark include:
1. Imperceptibility
2. Undetectability
3. Resistance to all signal manipulations
4. Extractability to prove ownership
5. Unambiguity
The watermark should be imperceptible in the manner that the changes made to cover object for
embedding the watermark should not create a very high order of distortion. That is the quality of
the cover object should remain unaffected despite the changes done in it for hiding the
watermark thereby, making the watermark imperceptible. The watermark should also be
undetectable when searched by any malicious user with an aim to destroy or remove it. Another
property that the watermark needs to exhibit is its resilience to the signal manipulations and other
deliberate attacks. It should be so embedded in the cover work that it is resistant to all changes
made in the cover work. Lastly, the watermark should be extractable to some acceptable extents
to prove the copyright ownership whenever required to do so. These attributes of the watermarks
have to be taken into account before developing the algorithm for its embedding and extraction.
Also, the watermark should be unambiguous so that no two parties may claim for the same
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media work. Watermark, when extracted, should be able to prove the copyright ownership most
efficiently.
1.3 Classification of Watermarking Techniques
The watermarking techniques used to embed information are dependent on the requirements of
the applications that the cover work is to be used for. So it is designed according to the type of
cover media, resilience to attacks and environment in which it is used. The taxonomy is shown in
figure 1. The division of the watermarking strategies has been done in following main streams on
the basis of:
1. Cover Media
2. Domain
3. Extraction strategy
4. Resistance to attacks
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Figure 1.1: Taxonomy of Watermarking Techniques
On the basis of cover media used: The watermarking algorithms are broadly classified into 5
categories depending on the cover work that is to be watermarked. These are:
1. Text
2. Image
3. Audio
4. Video
5. Software
In text watermarking algorithms, spacing between the letter, words and lines or the typing style
is manipulated in a manner to embed the watermark. The changes reflect the embedding of
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watermark in the document. Image watermarking scheme has been the most popular research
area in watermarking. Exhaustive research has been carried out in this direction. There are two
domains in which the watermarking is done namely:
1. Spatialdomain
2. frequency domain
In spatial domain, changes are made to the pixel values of the image in order to embed the
watermark which can be another image or any other signal. In frequency domain, transform is
applied to the image and then coefficients are changed to embed the watermark depending on the
frequency region in which the watermark needs to be hidden. This embedding of watermark is
dependent on the Human Visual System (HVS).
Audio watermarking is another domain of work where the watermark is embedded in the audio
signal to curb the unlimited piracy of the media. Audio watermarking is comparatively difficult
to implement due to the sensitivity of the Human Auditory System. The modifications are made
to amplitude values of the samples or to the transform coefficients when any transform is applied
to the audio signal.
Video watermarking involves the embedding to be done in the continuous image frames of the
video or to the audio part of the signal or to both. Since, human auditory system is more sensitive
to changes in amplitude so the watermark embedding is carried out in the pixel values of image
frames. Software watermarking is done in order to discourage software piracy. Watermark can
be embedded in the code part or in the data of the software.
Watermark can be some classified textual information which when extracted can prove the
copyright ownership. On the basis of domain: The watermarking algorithms can be broadly
classified into two categories:
1. Time/ spatial domain
2. Frequency/ Transform domain
In spatial domain, the watermark is embedded by directly modifying the values of cover object.
For example, in images the pixel values can be modified and in audio the amplitude values can
be manipulated. In transform domain, a transform is applied to the cover object and then
manipulations are done to the transform coefficients in the required frequency band. The main
transforms in common use are: Discrete Cosine Transform (DCT), Discrete Fourier Transform
(DFT), Discrete Wavelet Transform (DWT) etc.
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On the basis of extraction strategy: This classification is done on the basis of the fact whether the
original cover object or some extra information is required for watermark extraction. It is divided
into three broad categories:
1. Non blind techniques
2. Semi blind techniques
3. Blind techniques
In the non blind strategy the original cover work is required to extract the watermark. The main
disadvantage of this method is that extra bandwidth is required to send the original cover work as
well along with the watermarked work. In semi blind strategy, some information derived from
the original cover work, not exactly the original media is required for extracting the watermark.
This information can be any data derived from the media file. In the blind strategy, no extra
information is required for the extraction of the watermark. In comparison to blind strategy, non
blind watermarking algorithms are more resistant to attacks On the basis of resistance to attacks:
In this category of classification, watermarking scheme is again classified into three types:
1. Fragile
2. Semi fragile
3. Robust
The watermarking strategies come under the category of being fragile when they cannot sustain
the signal manipulation and intentional attacks. Semi fragile techniques can sustain some attacks
but they also fail against some of them. Robust strategies are those which are resistant to all the
deliberate and non deliberate attacks. They are capable of sustaining most of the attacks. That is,
the watermark can be successfully extracted or detected even if the cover work is corrupted with
attacks.
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1.4 Digital watermarking life-cycle phases
Figure 1.2 : Digital watermarking life-cycle phases
General digital watermark life-cycle phases with embedding-, attacking-, and detection and
retrieval functions
The information to be embedded in a signal is called a digital watermark, although in some
contexts the phrase digital watermark means the difference between the watermarked signal and
the cover signal. The signal where the watermark is to be embedded is called the host signal. A
watermarking system is usually divided into three distinct steps, embedding, attack, and
detection. In embedding, an algorithm accepts the host and the data to be embedded, and
produces a watermarked signal.
Then the watermarked digital signal is transmitted or stored, usually transmitted to another
person. If this person makes a modification, this is called an attack. While the modification may
not be malicious, the term attack arises from copyright protection application, where pirates
attempt to remove the digital watermark through modification. There are many possible
modifications, for example, lossy compression of the data (in which resolution is diminished),
cropping an image or video, or intentionally adding noise.
Detection (often called extraction) is an algorithm which is applied to the attacked signal to
attempt to extract the watermark from it. If the signal was unmodified during transmission, then
the watermark still is present and it may be extracted. In robust digital watermarking
applications, the extraction algorithm should be able to produce the watermark correctly, even if
the modifications were strong. In fragile digital watermarking, the extraction algorithm should
fail if any change is made to the signal.
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1.5 Purpose of Digital Watermarking
Watermarks added to digital content serve a variety of purposes. The following list details six
purposes of digital watermarking (Memon & Wong, 1998).
Ownership Assertion – to establish ownership of the content (i.e. image)
Fingerprinting – to avoid unauthorized duplication and distribution of publicly available
multimedia content
Authentication and integrity verification – the authenticator is inseparably bound to the
content whereby the author has a unique key associated with the content and can verify integrity
of that content by extracting the watermark
Content labeling – bits embedded into the data that gives further information about the content
such as a graphic image with time and place information
Usage control – added to limit the number of copies created whereas the watermarks are
modified by the hardware and at some point would not create any more copies (i.e. DVD)
Content protection – content stamped with a visible watermark that is very difficult to remove
so that it can be publicly and freely distributed Unfortunately, there is not an universal
watermarking technique to satisfy all of these purposes (Memon & Wong, 1998). The content in
the environment that it will be used determines the digital watermarking technique. The
following section describes some digital watermarking techniques.
1.6 Properties
For better activeness, watermark should be perceptually invisible within host media, statistically
invisible to unauthorized removal, readily extracted by owner of image, robust to accidental and
intended signal distortion like filtering, compression, resampling, retouching, crapping etc. For a
digital watermark to be effective for ownership, it must be robust, recoverable from a document,
should provide the original information embedded reliably and also removed by authorized
users.
All these important properties of digital watermarks are described as-
1. Robustness :The watermark should be robust such that it must be difficult to remove. The
watermark should be robust to different attacks. The robustness describes whether watermark
can be reliably detected after performing some media operations.
2. Perceptual transparency:This property describes that whether watermark is visible or
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invisible to human sensor organ. Perceptible watermarks are visible to human while
imperceptible are not. Imperceptible watermarks are such that content remains same after
applying digital watermarking technique.
3. Security: Security property describes that how easy to remove a watermark. This is generally
referred to as attack on watermarking. Attack refers to detection or modification of watermark.
4. Complexity: This is important property which is to be consider in real time applications like
video. Complexity property is concerned with amount of effort needed to extract or retrieve the
watermark from content.
5. Capacity : Capacity property of digital watermarks refers to amount of information that can
be embedded within the content. The important point is that more data is used in watermark,
watermark will become less robust.
In addition to these properties, watermarks are having some extra properties as unambiguity,
tamper resistance, inseparable from the works and able to undergo some transformation as
works.
1.7 Why to use it?
First important application come into mind is copyright protection of digital media.It is easy to
duplicate digital data exactly without quality loss. Similar to process in which artist signed their
painting with a brush to claim their copyrights, artist of today can watermark their work and hide
some information say their name in the image. Hence, embedded watermark will allow to
identify the owner of work. This concept is applicable to digital video and audio also. Especially,
distribution of digital audio over internet in MP3 format is currently a big problem. Digital
watermarking may be useful to setup controlled audio distribution and provide efficient means
for copyright protection, usually in collaboration with international registration bodies such as
IDDN(Inter Deposite Digital Number). In addition with copyright protection, Digital
watermarking is playing a important role in many fields of applications such as broadcast
monitoring, owner identification, transaction tracking, proof of ownership, fingerprinting,
content authentification, copy control, device control. Digital watermarks can also serve as
invisible labels and content link. For example, photo development labs may insert a watermark
into the picture to link the print to its negative.so, it is becomes easy to find out negative of a
print. All one has to do is to scan the print and extract the information from negative. In a
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completely different scenario, the digital watermarks may be used as a geometrical reference
which may be useful for programs such as Optical Character Recognition(OCR) software. The
embedded calibration watermark may improve the detection reliability of the OCR software
since it allows the determination of translation, rotation and scaling. Digital watermarking also
serves as a means of advertising within the digital media. For instance, the user may download
and view a digital image, use a watermark reader to extract the digital signature, then access a
web based directory to find the company’s name and up-to-date address, phone number and web
and e-mail address. Digital watermarks also serves the purposes of identifying quality and
assuring authenticity. A graphic or audio file bearing digital watermark can inform the viewer or
listener who owns to the item.
The technique Digital Watermarking is the recent research in the field of multimedia and internet
copyright protection field. There are various applications of digital watermarking as broadcast
monitoring, owner identification, proof of ownership, transaction tracking,content authentication,
copy control, device control and so on. Out of these, some important applications are described
as-
1.Broadcast monitoring
This application identifies that when and where works are broadcast by recognizing watermarks
embedded in these works. There are variety of technologies to monitor playback of sound
recording on broadcast. The digital watermarking is alternative to these technologies due to it’s
reliable automated detection. A single PC based monitoring station can continuously monitor to
16 channels over 24 hours with no human interaction. Resulted monitoring is assembled at
central server and is now available to interested one .The system can distinguish between
identical versions of songs, which are watermarked for different distribution channel. Such
system requires Monitoring infrastructure and watermarks to be present in content.Watermarking
video or music is planned by all major entertainment componies possessing closed networks.
2. Encoding
According to the thinking of major music companies and major video studios, encoding happens
at mastering level of sound recording. In such downstream, transactional watermarks are also
considered. Each song is assigned with unique ID from the identifier database.After completion
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of all mastering processes, ID is encoded in sound recording.To enhance encoding of audio or
video recordings requiring special processing, the human-assisted watermark key is available.
3. Copy and playback control
The data carried out by watermark may contain information about copy and display permissions.
We can add a secure module into copy or playback equipment to automatically extract the
permission information and block further processing if required.This approach is being taken in
Digital Video Disc(DVD).
4. Content authentication
The content authentication is nothing but embedding the signal information in Content. This
signature then can be checked to verify that it has not been alter. By watermarks, digital
signatures can be embedded into the work and any modification to the work can be detected.
CHAPTER 2
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Image Watermarking
A watermark is A pattern of bits inserted into a digital image file that identifies the file's
copyright information (author, rights, etc.). The name “watermark” is derived from the faintly
visible marks imprinted on organisational stationery.
Unlike printed watermarks, which are intended to be somewhat visible (like the very light
compass stamp watermarking this report), digital watermarks are designed to be completely
invisible.
Figure2.1: Image watermarking
The purpose of digital watermarks is to provide copyright protection for intellectual property that
is in digital format.
As seen above, Alice creates an original image and watermarks it before passing it to Bob. If
Bob claims the image and sells copies to other people Alice can extract her watermark from the
image proving her copyright to it.
The caveat here is that Alice will only be able to prove her copyright of the image if Bob hasn’t
managed to modify the image such that the watermark is damaged enough to be undetectable or
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Image 1
Alice
watermark
Send to Bob
copies
Watermark Image
added his own watermark such that it is impossible to discover which watermark was embedded
first.
2.1 Technical Details
Digital watermarking technology makes use of the fact that the human eye has only a limited
ability to observe differences. Minor modifications in the colour values of an image are
subconsciously corrected by the eye, so that the observer does not notice any difference.
While vendors of digital watermarking schemes do not publicly release the exact methods used
to create their watermarks, they do admit to using the following basic procedure (with obvious
variations and additions by each vendor).
A secret key (string or integer) produces a random number which determines the particular
pixels, which will be protected by the watermarking. The watermark is embedded redundantly
over the whole image, so that every part of the image is protected.
Figure2.2 : Working
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One way of doing this is by “Patchwork”. This technique uses a random number generator to
select n pairs of pixels and slightly increases or decrease their luminosity (brightness level). Thus
the contrast of this set is increased without any change in the average luminosity of the image.
With suitable parameters, Patchwork even survives compression using JPEG.
Although the amount of secret information has no direct impact on the visual fidelity of the
image or the robustness of the watermark, it plays an important role in the security of the system.
The key space, that is the range of all possible values of the secret information, x must be large
enough to make exhaustive search attacks impossible.
In the process of extracting the watermark, the secret key is used to identify the manipulated
pixels and finally to decode the watermark.
As an example of poor engineering, an early version of Digimarc’s watermarking software gave
each licensed user an ID and a two-digitnumeric password, which were issued when she registers
with Digimarc and pays for a subscription.
The password checking mechanism could easily be removed by flipping a particular “flag” bit
and the passwords had only 99 possibilities so it was short enough to be found by trial and error.
A deeper examination of the image also allowed a villain to change the ID and thus the copyright
of an already marked image as well as the type of use (such as adult -> general public content).
Before embedding a mark, watermarking software usually checks whether there is already a
mark in the picture, but this check can be bypassed fairly easily with the result that it is possible
to overwrite any existing mark and replace it with another one.
The quality of digital watermarks can be judged in two ways; firstly it must be able to resist
intentional and unintentional attacks and secondly the embedded watermark must not detract
from the quality of the image.
The higher the resistance of a watermark against attacks, the higher the risk of the quality of the
image being reduced, and the greater the chance of obvious visual artefacts being created.
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2.2 Methods used to test Watermark Robustness
These are some of the methods that can be used to test whether a watermark can survive different
changes to the image it is embedded in.
Compare this Original Image with the attacked images below, and see if you can spot any
changes in quality.
Horizontal Flipping
Many images can be flipped horizontally without losing quality. Few watermarks survive
flipping, although resilience to flipping is easy to implement.
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Rotation & Cropping
A small rotation with cropping doesn’t reduce image quality, but can make watermarks
undetectable as rotation realigns horizontal features of an image used to check for the presence
of a watermark.
The example has been rotated 3 degrees to the right, and then had its edges cropped to make the
sides straight again.
JPEG Compression/Re-compression
JPEG is a widely used compression algorithms for images and any watermarking system should
be resilient to some degree to compression or change of compression level e.g. from 71% to 70%
in quality like the example .
Scaling
Uniform scaling increases/decreases an image by the same % rate in the horizontal and vertical
directions.
Non-uniform scaling like the example at left increases/decreases the image horizontally and
vertically at different % rates. Digital watermarking methods are often resilient only to uniform
scaling.
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Dithering
Dithering approximates colors not in the current palette by alternating two available similar
colors from pixel to pixel. If done correctly this method can completely obliterate a watermark,
however it can make an image appear to be “patchy” when the image is over-dithered (as in the
elbow area of the image).
Mosaic
A mosaic attack doesn’t damage the watermarked image or make it lose quality in any way, but
still enables the image to be viewed in eg: a web browser by chopping the image into subsections
of equal size and putting it back together again.
To the viewer a “mosaic” image appears to look the same as the original but a web crawler like
DigiMarc’s MarcSpider sees many separate images and doesn’t detect that these separate images
are parts of a watermarked image.
This means that the watermark cannot be detected, as a problem common to all image
watermarking schemes is that they have trouble embedding watermarks into small images, (less
than 256 pixels in height or width).
Stirmark
StirMark is the industry standard software used by researchers to automatically attempt to
remove watermarks created by Digimarc, SysCoP, JK_PGS (TALISMAN project – É.P.F.L.
algorithm), Signum Technologies and EIKONAmark.
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Stirmark attacks a given watermarked image using all the techniques mentioned in this report as
well as more esoteric techniques such as low pass filtering, gamma correction,
sharpening/unsharpening etc.
All vendors of digital watermarks have their products benchmarked by Stirmark and as of
August 2001, no watermark from any vendor survives the test, ie: the watermarks are all
removed without degradation to image quality occurring.
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Chapter 3
Audio Watermarking
With the development of the internet and increase in the need for the security and integrity of the
data in transit on the network, watermarking has gained a great interest. With this, the protection
of intellectual property rights has become one of the areas of main concern. The main work in
the field of watermarking has been focused on images and videos. Only a few audio
watermarking schemes have been reported till date. Digital audio watermarking is the scheme of
embedding some relevant information in the audio signal so as to prove the copy right
ownership. Audio watermarking is difficult to implement as compared to image watermarking
due to high sensitivity of human auditory system (HAS). The general strategy to implement
audio watemarking is diagrammatically given as:
Figure 3.1 : Audio Watermarking: General Strategy
The simplest visualization of requirements of the audio watermarking algorithms is the magic
triangle. Its vertices are inaudibility, robustness to attacks and watermark data rate. This triangle
is a perfect visual representation of the trade-offs between the watermark capacity and
robustness, keeping the perceptual quality of the watermarked audio at an acceptable level. It is
certainly not possible to attain high robustness and high watermark data rate simultaneously.
Hence, to achieve robustness against attacks,
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Figure 3.2 : Magic Triangle
capacity of the watermark has to be compromised. The requirements that have to be
satisfied among all the three are very much application dependent. As for an instance
in steganography applications, the algorithms have to attain robustness to attacks.
3.1 Human Auditory System
The Human Auditory System is very sensitive to slightest changes in the audio due to its wider
dynamic range. Hence watermarking of audio signals is more challenging as compared to
watermarking of images or video. The HAS perceives sounds over a range of power greater than
109:1 and a range of frequencies greater than103:1. The HAS is highly sensitive towards
Additive White Gaussian Noise (AWGN). The slight perturbations in a sound file are detected
even if they are as low as one part in ten million or 80dB below ambient level. This is because
the human ear can perceive amplitude distortion but it is relatively insensitive to phase distortion.
On the other hand, HAS has a fairly small differential range which means loud sounds can mask
out the weaker sounds .
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The human ear acts as a frequency analyser that maps signal frequencies to locations along the
basilar membrane. The HAS is generally modelled as a non uniform filter bank with
logarithmically widening bandwidth for higher frequencies. The bandwidth of each filter is set
according to the critical band, which is defined as the bandwidth in which subjective response
changes abruptly. Hence, HAS is modelled as a bandpass filterbank, containing strongly
overlapping bandpass filters with bandwidths around 100 Hz for bands with a central frequency
ranging between 500Hz to 5000 Hz for bands placed at high frequencies.
The main properties of the HAS mainly used in watermarking algorithms are frequency
(simultaneous) masking and temporal masking. Masking properties are exploited to embed
additional bit stream into the cover audio signal without generating the audible noise thus
keeping the watermark concealed.
3.2 Types of Audio Watermarking Techniques
Digital audio watermarking techniques can be broadly classiffied into 2 categories based
on the domain in which the watermarking is done:
1. Time domain
2. Frequency domain
Figure 3.4 : Taxonomy of Audio Watermarking Techniques
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In time domain audio watermarking schemes, the watermark is embedded by modifying the
audio signal itself. In transform domain, modifications are done on the transform coefficients of
the components of the audio signal. Time domain techniques can be further classified into two
categories (a) when the audio signal samples are modified for embedding the watermarking
(LSB Decoding method, Quantization method, phase watermarking method), (b) when inaudible
noise (watermark) is added on to the audio signal (addition of pseudo random sequence, echo
hiding method, patchwork method). The following sections will discuss various audio
watermarking techniques and the affect of various audio signal attacks on the robustness of the
watermark when embedded by these techniques.
3.2 Time Domain Techniques
When the watermark is directly embedded into the audio signal then they come under this
category and they are broadly classified into two parts on the basis of how the watermark is
embedded into the signal.
1. LSB Decoding Method
The simplest and most straight forward technique of embedding the watermark is to embed it
into the Least Significant Bits of the audio signal. Given the extraordinary high channel capacity
of using the entire audio signal for transmission, the watermark can be embedded into it multiple
number of times. The audio signal is first divided into segments and a subset of the segments is
selected. The LSBs of these segments are modified according to the bit of the watermark that is
to be embedded. Extraction of the watermark is performed by extracting the least significant bits
of the selected segments. If the extracted bits and the inserted bits match then the watermark is
successfully detected. It is a blind algorithm the original audio signal is not required for detection
of the watermark.
The advantages of this method are:
(a) As it is simple to implement, its algorithmic delay is very less.
(b) It has very high watermark capacity as stated earlier.
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Disadvantages being:
(a) It is extremely less robust due to the fact that random changes of the LSBs destroy the coded
watermark.
(b) It is quite unlikely that the watermark would survive the analog to digital conversion and
vice versa.
2. Quantization Method
This scheme divides an audio signal into samples and then quantizes a value for each sample.
Then the quantized value of each sample is modified based on the watermark bit to be
embedded. In the scalar quantization method a quantization step is decided on whose basis the
quantized value of the sample is generated by using the quantization function. It is with the use
of quantization step only that the value of the sample is modifiied with regard to the bit being
inserted. The detection process is exactly the reverse of the insertion process.
The main advantages of this method are:
(a) It is very simple to implement
(b) It is a blind algorithm.
The disadvantage is:
(a) It cannot survive the noise attacks if the additive noise is larger than the quantization step.
This method can also be characterized as one which uses the information of the audio signal for
embedding the watermark.
3. Addition of Pseudo Random Sequence
In this scheme, the watermark is simply considered to be pseudo random sequence.This
technique takes into account the characteristics of the psycho acoustic model such that added
sequence does not cause any audible effect on the audio signal.
Before embedding the watermark, it is shaped in such a manner that its addition to the signal is
not heard. The shaping of watermark can be done in many ways, one of them is filtering. In this
method, the audio signal is again divided into samples and the shaped pn sequence is added to
each of the samples of the signal or some of the selected samples. The method of addition of the
watermark can be additive, multiplicative etc. In the extraction process, the audio signal is again
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divided into samples and the watermark is extracted from the selected ones or all of them by the
procedure reverse of what was followed for embedding. Now the extracted and the original and
the extracted watermark can be compared to check for the successful detection.
The advantages of this algorithm are:
(a) The watermark can be repeatedly embedded in the audio signal.
(b) It is quite robust against attacks.
The disadvantage being:
(a) The transmission cost of the audio signal goes very high.
4. Echo hiding method
Echo hiding embeds the data into the audio signal by introducing an echo in time
domain. The nature of such echoes is to add resonance to the host audio.
x(n) = s(n) + a:s(n - d)
Here only 1 echo sound is being added but multiple echoes can also be added.
Here in this method the host audio signal is divided into smaller portions. Each portion can be
considered as an independent signal. Now embedding of the watermark into these independent
signals takes place by introducing the bit delays.
As for an instance, binary messages are added by echoing the original signal with 2 delays, either
a d0 sample delay for bit 0 or a d1 sample delay for bit 1. Extraction of the embedded message
involves the detection of the delay. Cepstrum or Autocepstrum analysis are used for these
purposes.
The advantages of Echo hiding method are:
(a) It is quite imperceptible and usually makes the sound rich.
(b) This is a blind algorithm and is highly robust against desynchronization attacks.
The main disadvantages of this method are:
(a) Its increased complexity due to the use of cepstrum analysis for detection.
(b) As the human auditory system is quite sensitive, so echoes ca be very easily detected and
they provide a clue for malicious attack.
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5. Patchwork method
This scheme embeds a special statistic into the audio signal. Two patches are pseudo randomly
selected from the original audio signal. These two patches are nothing but the group of some
samples each. In the simplest patchwork strategy,a constant value d is added to one patch and
subtracted from another. Apart from the additive strategy, multiplicative operations can also be
used for the implementation of the patchwork method in which a single bit of the watermark is
embedded into the signal by multiplying or dividing the sample values of one patch thus,
leaving the other patch intact. The watermark is extracted at the receiver end by the comparison
of energies of the two patches so as to say the expected values of the samples of the two patches
are compared. In case of the addition and subtraction operated patchwork scheme, the difference
of the sample values of the patches is compared with the threshold value to decide whether the
samples contain the watermark or not. The threshold value is decided with the constant value that
is used while embedding the watermark .
Its greatest advantage is:
(a) Since the algorithm does not use the original audio signal for watermark
extraction, it is a blind algorithm.
(b) This scheme can also be implemented in transform domain [26] as well and
in that case the modifications would be done on the transform coefficients of
the samples in the patches .
Disadvantage of this scheme is:
(a) It is less robust against attacks if position of patches is known.
6. Spread Spectrum method
The spread spectrum technique encrypts information by spreading the encrypted data across a
large frequency spectrum. In this technique the watermark is first shaped and then it is spread
over the entire audio signal by the use of various spread spectrum techniques. The spread
spectrum technique can also be implemented in the transform domain. In Direct Sequence
Spread Spectrum techniques, spreading is accomplished by modulating the original signal with a
sequence of pseudo random binary pulses known as chips. In the embedding process, the audio
data is coded as a binary string. The code is modulated by a carrier wave and multiplied by the
pseudo-random noise sequence, having a wide frequency spectrum. It spreads the frequency
26
spectrum [29] of the data over the available frequency band. This spread data sequence is
attenuated and added to the original file. For extraction the watermarked signal is again
multiplied by the same pseudo-random noise sequence. The watermark is spread over so many
components of the signal
so that the energy of any component is very small and certainly undetectable.
The advantages of this technique are:
(a) It is a simple to implement.
(b) It is a blind algorithm.
Its greatest disadvantage is:
(a) This method is highly fragile against de-synchronization attacks.
3.3 Frequency Domain Techniques
Audio signals are transformed from time domain to frequency domain to enable effective
embedding of the watermark. Transform domain techniques allow the embedding of the
watermark in the perceptually significant components of the audio signal. The transform
domain techniques are more robust against attacks as compared to the time domain techniques
but the drawback being the high computation requirement. Various time domain techniques can
be incorporated with the transform domain techniques to make more robust methods of audio
watermarking.
1. DCT based Watermarking
Watermark message is embedded into the host audio by modifying the DCT coefficients, which
can be regarded as addition of noise to the original audio signal. Audio signals is divided into
frames and DCT is applied to them individually. Shaped watermark signal is then added to the
DC or AC coe_cients of the transformed audio signal. Then inverse DCT is applied to the
frames. The DCT transform divides the signal into three frequency regions namely , low mid and
high. The watermark is fragile when embedded in the low or high frequency region so for
robustness, it is embedded in the mid frequency range. The other reason for not embedding the
watermark in the low frequency region is that it causes audible changes to the signal thereby,
destroying its fidelity. In case of embedding the watermark in high frequency region, the
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problem is of robustness only. The chances of the removal of the watermark are very high by
simple signal processing operations.
For extracting the watermark, DCT needs to be applied to the signal and then from the selected
frames the watermark is extracted by following the procedure reverse to that used for
embedding.
2. DFT based Watermarking
The methodology to embed the watermark in the audio signal is same as DCT. The audio signal
is divided into frames and DFT is applied on them individually. Some or all of the frames can be
used for embedding the watermark. In case the watermark is to be embedded in some frames
then one way for the selection of these frames is on the basis of a secret key. This key is used at
the time of extraction also for taking out the selected frames. The application of DFT divides
the signal into two parts of phase and magnitude. The watermark is embedded into any of these
parts of the DFT coeffcients depending upon the requirement of the application. Prominently the
embedding is done in magnitude part only. Perform the inverse DFT on the frames to reconstruct
the audio signal. For extraction again the same DFT is applied to the signal and from the selected
frames watermark is extracted.
The advantages of this technique are:
(a) It is highly robust against various signal processing attacks.
(b) It is a blind algorithm.
(c) This scheme is more robust to attacks than DCT based watermarking scheme.
The disadvantage is:
(a) The complexity of the procedure involved for watermarking and extraction
is quite high.
3. DWT based Watermarking
DWT based watermarking schemes are on the same pattern as DCT based schemes. The audio
signal is transformed by wavelet transforms using wavelet filters. The common filters for
watermarking are Daubechies Orthogonal Filters, Haar Wavelet Filter and Daubechies Bi-
Orthogonal Filters. The signal is decomposed into several frequencies by these filters. On single
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level decomposition, the signal is decomposed into two parts, high frequencies and low
frequencies. The part containing low frequencies is again decomposed into two parts, high
frequencies and low frequencies. The number of levels in which the signal can be decom-
posed depends upon application and length of signal. The decomposed data thus obtained gives
DWT coefficients. The original signal can again be reconstructed by applying the inverse DWT
scheme.
3.4 Methods used to test Watermark Robustness
The most common method of watermarking audio is to mark every xth
bit in an audio file
depending on the random generator seed calculated from the watermarking key applied to the
audio. These are some of the ways watermarks can be removed from audio files MPEG1 Layer
III (MP3) audio compression
A digital audio compression algorithm that achieves a compression factor of about twelve while
preserving sound quality. What this lossy compression does is remove the frequencies not heard
by the human ear from the audio. If a raw audio file is converted to MP3 at a bit-rate of 128kbps
than roughly 90% of the frequencies are removed. This means that a search for the watermark
needs to find an unaltered length of samples that contains at least 2 watermarked bits to prove the
watermarks existence.
Audio Restoration programs
Audio restoration programs are designed to remove hisses, crackles and pops from audio
recordings. They do this by searching through the wavelength, removing samples that don’t “fit
in” amongst neighbouring samples, and replacing them with an average of the two neighbour
samples. Although the removal of digital watermarks is obviously not a purpose of these
programs, they work remarkably well at doing so as the sample bits inserted to watermark the
audio don’t fit in with their surrounding pixels, and are therefore removed.
Echo Hiding Removal
Echo hiding relies on the fact that we cannot perceive short echoes, eg: 1 millisecond(ms) and
embeds data into a cover audio signal by introducing an echo characterised by its delay and its
relative amplitude compared to surrounding samples. The echo delays are chosen between 0.5
ms and 2 ms and the best relative amplitude of the echo is around 0.8 ms. However specialised
29
software which looks for echoes with a length between 0.5 ms and 2 ms 7(as seen below), can be
used to detect and remove these echoes without effecting sound quality.
Zitter
The simplest and most effective attack on any audio watermarking scheme is to add jitter to the
signal. ”In our first implementation, we split the signal into chunks of 500 samples, either
duplicated or deleted a sample at random in each chunk (resulting in chunks of 499 or 501
samples long) and stuck the chunks back together. This turned out to be almost imperceptible
after altering, even in classical music; but the jitter prevents the marked bits from being located”,
and therefore the watermark is obliterated.
In his paper titled “Audio watermarking: Features, Applications And Algorithms“, Michael
Arnold agrees with the Cambridge team stating that
“one of the greatest challenges [of watermarking] is the robustness against the so-called jitter
attack”.
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CHAPTER 4
ADVANTAGES AND DISADVANTAGES
4.1 Advantages of digital watermarking
The field of digital watermarking is not restricted to digital images. This technique time and
frequency masking properties of human ear to conceal the watermark and make it unaudible.
There are some benefits of this technique as-
1. Uniquely identifies author of copyrighted works.
2. Robust design of digital waetrmark withstand pirating attacks.
3.Embedding watermark is easy.
4. Implementation on PC platform is possible.
There are some military and civilian applications of digital watermarking also.
Military applications
1. Intelligence activities.
2.Traitor tracing.
3. Image tampering detection.
Civilian applications
1. Copyright protection of each digital media in hardcopy or on internet.
2. Intelligent web browsers.
3. Law enforcement for chain of evidence.
Some special watermarking technique uses color separation. So watermarks appears in only one
of the color bands. Therefore watermarks becomes strongly invisible. Whenever the colors are
separated from printing then watermarks becomes visible. This approach is advantageous to
journalists to inspect digital pictures from a photo stockhouse before buying an un-watermarked
versions.
There is an important advantage of invisible fragile watermarks. With such invisible fragile
watermarks, implementation of web based image authentication This web based authentication
includes watermark embedding and authentication system. In case of watermark embedding
system, it is installed in server as application software that any authorized user who access to
server can generate watermark image.The distribution can be done through any network as FTP,
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e-mail etc. Once image is distributed to externally, client can get authentication web page to get
verification of images. Digital watermarking techniques is having advantages as we seen
earlier.It also have some limits also.
4.2 Disadvantages of digital watermarking
Digital watermarking is recent research field, therefore it’s intrinsic limitations are not
understood yet. The blind watermarking algorithm which is really robust is not in existence
today. Another disadvantage is that owner can erase the watermark. By knowing the exact
content of watermark and algorithms to embeds and retrieve it. It is always possible to make it
unreadable without any significant degradation of the data. Again it is not clear that. if this
drawback will be got around in future, in the meantime ,the possibility of erasing the watermark
or its part ,once it’s content is known must be taken into account when designing a copyright
protection system. As a matter of fact, if anyone is allow to read the watermark, then anyone can
erase it by knowing the embedding algorithm. In some researches, the conclusion comes that not
all watermarking techniques will be useful in resolving ownership disputes. Watermarking does
not prevent image copying as much as it simply makes copied images easier to track down and
detect ownership.
Some watermarks vanish if someone manipulates the image in a program like Photoshop. The
watermarks have been known to weaken or disappear by the time the images were processed for
the Internet. Resizing, compressing and converting images from one file type to another may add
noise to an image or diminish its watermark in such a manner that the watermark becomes
unreadable.
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CHAPTER 5
FUTURE OF DIGITAL WATERMARKINGThe field of digital watermarking is still evolving and is attracting a lot of research interest. The
watermarking problem is inherently more difficult that the problem of encryption, since it is
easier to execute a successful attack on a watermark. In cryptography, a successful attack often
requires deciphering an enciphered message. In the case of digital watermarking, merely
destroying the watermark, usually by slightly distorting the medium containing it, is a successful
attack, even if one cannot decipher or detect any hidden message contained in the medium.The
enormous popularity of the World Wide Web in the early 1990's demonstrated the commercial
potential of offering multimedia resources through the digital networks. Since commercial
interests seek to use the digital networks to offer digital media for profit, they have a strong
interest in protecting their ownership rights.
Digital watermarking has been proposed as one way to protect such interests. Though much
research remains before watermarking systems become robust and widely available, there is
much promise that they will contribute significantly to the protection of proprietary interests of
electronic media. Collateral technology will also be necessary to automate the process of
authentication, non-repudiable transmission and validation. An exhaustive list of watermarking
applications is of course impossible. However, it is interesting to note the increasing interest in
fragile watermarking technologies. Especially applications related to copy protection of bills
with digital watermarks. Various companies have projects in this direction solutions will soon be
available. In addition to technological developments, marketing and business issues are
extremely important and require in-depth analysis and strategic planing. It is very important to
prepare the industry to the usage of digital watermarks and and it is very likely that fully
functioning to convince them of the added value their products can gain if they employ digital
watermarking technologies.
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CHAPTER 6
CONCLUSION
The large need of networked multimedia system has created the need of COPYRIGHT
PROTECTION. It is very important to protect intellectual properties of digital media. Internet
playing an important role of digital data transfer. Digital watermarking is the great solution of the
problem of how to protect copyright. Digital watermarking is the solution for the protection of
legal rights of digital content owner and customer.
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CHAPTER 7
REFERENCE
[1] http://www.wekipedia.org
[2] Kim, H.J., Audio Watermarking Techniques, Paci_c Rim Workshop on Digital
Steganography, Japan, July 2003.
[3] Arnold M., Audio watermarking: Features, Applications and Algorithm, IEEE
International Conference on Multimedia and Expo., vol. 2, pp. 1013-101, 2001.
[4] Cano, R.G., et al, Analysis of Watermarking Schemes, 2nd International
Conference on Electrical and Electronics Engineering (ICEEE) and XI Conference
on Electrical Engineering, Mexico, 2005.
[5] Arnold M, Audio Watermarking, Dr. Dobb's Journal, vol. 26, Issue 11, pp. 21-26,
2001.
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