Digital Watermarking for Images Aarathi Raghu CS 265 Spring 2005.
-
date post
21-Dec-2015 -
Category
Documents
-
view
218 -
download
3
Transcript of Digital Watermarking for Images Aarathi Raghu CS 265 Spring 2005.
![Page 1: Digital Watermarking for Images Aarathi Raghu CS 265 Spring 2005.](https://reader033.fdocuments.us/reader033/viewer/2022042717/56649d535503460f94a300ff/html5/thumbnails/1.jpg)
Digital Watermarking for Images
Aarathi Raghu
CS 265
Spring 2005
![Page 2: Digital Watermarking for Images Aarathi Raghu CS 265 Spring 2005.](https://reader033.fdocuments.us/reader033/viewer/2022042717/56649d535503460f94a300ff/html5/thumbnails/2.jpg)
Agenda
1. Motivation
2. What is digital watermarking?
3. DCT
4. A Semi-fragile watermarking algorithm
5. Attacks and countermeasures
6. Conclusion
![Page 3: Digital Watermarking for Images Aarathi Raghu CS 265 Spring 2005.](https://reader033.fdocuments.us/reader033/viewer/2022042717/56649d535503460f94a300ff/html5/thumbnails/3.jpg)
Motivation
Analog Digital
Photographs JPEG images
Distribution net required
Free to distribute using internet
Hard to modify Easily modifiable
Some level of copyright protection
No copyright protection
![Page 4: Digital Watermarking for Images Aarathi Raghu CS 265 Spring 2005.](https://reader033.fdocuments.us/reader033/viewer/2022042717/56649d535503460f94a300ff/html5/thumbnails/4.jpg)
Digital Watermarking
Process of embedding information Information embedded is :
• Imperceptible
• Secure
• Robust
Semi-fragile watermarking– Uses:
• Tamper detection
• Image authentication
Scenario
![Page 5: Digital Watermarking for Images Aarathi Raghu CS 265 Spring 2005.](https://reader033.fdocuments.us/reader033/viewer/2022042717/56649d535503460f94a300ff/html5/thumbnails/5.jpg)
Concepts
Compression is inevitable to accommodate
disk space, bandwidth and transmission time.
Based on:– Redundancy reduction– Irrelevancy reduction
![Page 6: Digital Watermarking for Images Aarathi Raghu CS 265 Spring 2005.](https://reader033.fdocuments.us/reader033/viewer/2022042717/56649d535503460f94a300ff/html5/thumbnails/6.jpg)
Discrete Cosine Transform(DCT) Divides image into parts based on the visual quality
of the image
Input image is N*M f(i,j) = intensity of pixel in row i and column j F(u,v) is DCT coefficient in DCT matrix Larger amplitudes closer to F(0,0) Compression possible because higher order
coefficients are generally negligible
![Page 7: Digital Watermarking for Images Aarathi Raghu CS 265 Spring 2005.](https://reader033.fdocuments.us/reader033/viewer/2022042717/56649d535503460f94a300ff/html5/thumbnails/7.jpg)
DCT coding system
image
DCT Transformation
8*8 DCT
Quantization
Entropy encoding
Lossy compressed data
![Page 8: Digital Watermarking for Images Aarathi Raghu CS 265 Spring 2005.](https://reader033.fdocuments.us/reader033/viewer/2022042717/56649d535503460f94a300ff/html5/thumbnails/8.jpg)
Semi Fragile Watermark (LPD)
Designed by Lin, Podilchuk, Delp Watermark:Pseudo-random zero-mean, unit
variance Gaussian distributed numbers Constructed in DCT domain Watermark embedded in each DCT block
selectively
![Page 9: Digital Watermarking for Images Aarathi Raghu CS 265 Spring 2005.](https://reader033.fdocuments.us/reader033/viewer/2022042717/56649d535503460f94a300ff/html5/thumbnails/9.jpg)
Semi Fragile Watermark (ctd.)
High frequency coefficients and DC coefficient – unmarked
Inverse DCT produces spatial domain watermark W
Y = X + ßW, where ß is the strength
![Page 10: Digital Watermarking for Images Aarathi Raghu CS 265 Spring 2005.](https://reader033.fdocuments.us/reader033/viewer/2022042717/56649d535503460f94a300ff/html5/thumbnails/10.jpg)
Watermark Detection
Done block-by-block (col)(B(x,y))=B(x,y)-B(x+1,y) if x E {1,2, ….,
blocksize –1}, 0 otherwise (row)(B(x,y))=B(x,y)- B(x,y+1) if y E {1,2,
……,blocksize –1}, 0 otherwise Tb*= [(col)(Tb(x,y)) | (row)(Tb(x,y))] Wb*= [(col)(Wb(x,y)) | (row)(Wb(x,y))] C = (Tb*.Wb*)
sqrt ((Tb*.Tb*) (Wb*.Wb*))
![Page 11: Digital Watermarking for Images Aarathi Raghu CS 265 Spring 2005.](https://reader033.fdocuments.us/reader033/viewer/2022042717/56649d535503460f94a300ff/html5/thumbnails/11.jpg)
Block classification
Correlation statistic, C, is compared to a threshold T
C > = T : Block is authentic C < T : Block is altered
![Page 12: Digital Watermarking for Images Aarathi Raghu CS 265 Spring 2005.](https://reader033.fdocuments.us/reader033/viewer/2022042717/56649d535503460f94a300ff/html5/thumbnails/12.jpg)
Example
Detection
Original image Altered image
![Page 13: Digital Watermarking for Images Aarathi Raghu CS 265 Spring 2005.](https://reader033.fdocuments.us/reader033/viewer/2022042717/56649d535503460f94a300ff/html5/thumbnails/13.jpg)
Attacks
Removal attacks Geometric attacks Cryptographic attacks Protocol attacks
![Page 14: Digital Watermarking for Images Aarathi Raghu CS 265 Spring 2005.](https://reader033.fdocuments.us/reader033/viewer/2022042717/56649d535503460f94a300ff/html5/thumbnails/14.jpg)
Precautions
Watermark should be present over more number of pixels
Used keys should be secure Use of collusion-secure watermarks Watermarks should be non-invertible Possible attacks need to be foreseen
![Page 15: Digital Watermarking for Images Aarathi Raghu CS 265 Spring 2005.](https://reader033.fdocuments.us/reader033/viewer/2022042717/56649d535503460f94a300ff/html5/thumbnails/15.jpg)
References
1. ftp://skynet.ecn.purdue.edu/pub/dist/delp/ei00-water/paper.pdf
2. http://www-nt.e-technik.uni-erlangen.de/~su/seminar/ws99/slides/amon.pdf
3. http://www.lnt.de/~eggers/texte/IEEEcom2.pdf
4. http://www.acm.org/crossroads/xrds6-3/sahaimgcoding.html