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Watermarking schemes

Digital watermarkingtechniques

Visible watermarking

LSB

Spatial watermarking

DCT based watermarking (Cox)

Wavelet watermarking

QIM watermarking

Remember

From previous classes

Principle of Digital watermarking

Embedded hidden information, which travelswith the watermarked data, even aftercopying and redistribution.

How can information be hidden in digitaldata? Human perception is imperfect

Make modification to the original data without

changing its perceptual quality, exploit maskingprinciple (JND).

Modifications can be detected via signalprocessing.

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Text document watermarking

Text Document Watermarking

Two methods to hide information1) in the semantics; in the meaning and

ordering or the words2) in the format

* In the layout and the appearance

- Example of word shifting coding -

Text Document Watermarking;Three coding methods

1) Line shift coding*Assumption; lines are uniformly spaced doesnt need original for watermark extraction

2) word-shift coding

*Assumption; space between words are usually variable needs original for Watermark extraction

3) feature coding; slightly modifies the features

Goal: making watermark removal more expensive thanobtaining the right to copy from the copy right owner

Image watermarking

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Visible watermarking

Enhanced copyright protection: Digital data are made available through Internet

and the content owner is concerned that theimages will be used commercially.

Ownership mark, visible but not preventingother legal uses (e.g. scholarly research).

To indicate ownership originals: Digital data available for free.

Visible watermarking

From Watson web page: http://www.research.ibm.com/journal/rd/402/mintzer.html

Watson method

the watermark as unobtrusive as possible, yetreadily visible.

When a pixel is changed by our watermarking, thebrightness is reduced, while the hue and saturationare held constant.

In applying the watermark, we adjust thewatermarking's change of brightness to darken imagepixels by the same amount perceptually, whether

the pixels are light or dark.

Visible Watermarking

M. Kankanahalli, et. al., A daptive Visible Watermarking of Images, Proc. of IEEE Int. Conf.on Multimedia Computing Systems, ICMCS-99, Centro Affari, Florence, Italy, June 1999.

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Digital watermarkingtechniques

Visible watermarking

LSB

Spatial watermarking

DCT based watermarking (Cox)

Wavelet watermarking

QIM watermarking

Least Significant Bit

Substitution Techniques: Substitute redundant parts of a cover with a secret

message Choose a subset of cover elements and substitute least

significant bit(s) of each element by message bit(s) Message may be encrypted or compressed before hiding A pseudorandom number generator may be used to spread

the secret message over the cover in a random manner

Easy but vulnerable to corruption due to smallchanges in carrier

Example:LSB Encoding

Original Image Watermark

Replace 4 and 7 LSBs ofOriginal

4 LSBs Watermarked 7 LSBs Watermarked

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LSBDigital watermarkingtechniques

Visible watermarking

LSB

Spatial watermarking

DCT based watermarking (Cox)

Wavelet watermarking

QIM watermarking

Additive watermarking Add a weak signal (mark) representing ownership in host media

The weak signal is known to detector Detection by correlating a test copy with the watermark signal

Invisibility: Watermark signals with structural patterns can be easily perceived

than random noisy signals Robustness:

Watermarks added to perceptually insignificant components caneasily be distorted

Try

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Detection

Random Noise

Generator

YesKe y

CorrelatorGain

FactorX

+

T

No

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