Watermarking Techniques Digital Rights Seminar © April 28, 2006 Mahmoud El-Gayyar

First Part Watermarking Techniques in Spatial Domain Mahmoud El-Gayyar

* AGENDA * * First Part: Introduction a.Elements of a WM system b.Watermarking Requirements c.Watermarking Techniques * Second Part: A Fragile WM Technique a.Fragile Watermarking b.Fragile WM scheme + * Summary

Introduction -- Elements of a WM system * Elements of a WM System * Watermark Generator Watermark Generator Information Coder Information Coder Embedder Communication Channel Communication Channel Detector Signal Processing Signal Processing Watermark Generator Watermark Generator Information Coder Information Coder KgKg S0S0 S0S0 SwSw S’ w KK KgKg S0S0 W0W0 W0W0 WW W’ back

Introduction – WM Requirements * WM Requirements * 1. Security. a.Secrecy of WM b.Resist malicious attacks 2. Imperceptibility 3. Capacity 4. [Robustness] Robustness Capacity Imperceptibility

Introduction – WM Techniques * WM Techniques * Spatial DomainFrequency Domain Computation Cost LowHigh RobustnessFragileMore Robust Perceptual Quality High ControlLow Control Capacity High (depend on the size of the image) Low (1/16 of the host image) Example of Applications Mainly Authentication Copyright Protection

* AGENDA * * First Part: Introduction * Second Part: A Fragile WM Technique a.Fragile Watermarking b.Fragile WM scheme i.Symbol Definition ii.Embedding Algorithm iii.Detection Algorithm iv.Experiment on Attacks * Summary

Part 2 – Fragile WM * Fragile Watermarking * What is Fragile Watermarking? Type of Attack (Host Media Forgery) Unique Features: 1. High resolution tampering localization. 2. Tampering detection with low false positive. 3. Gemotric manipulation detectability. 4. Attack Identification. 5.Blind detection. 6.Proper Embedding Sequence: selection of dependency is limited to the previously watermarked portion of the image.

Part 2 – WM Scheme * WM Scheme * We will discuss a Fragile WM scheme depends on both of the contextual information and non- deterministic information to perform WM. Y.Yuan and C.Tsun. IEEE 2004 (17 th international conference of pattern recognition) Contextual (dependency) information: From other portions of the image. Non-deterministic information: randomly chosen parameters to produce a unique signature. link link Different non-deterministic signature for two identical blocks at the same position of two images.

Part 2 – WM Scheme – Symbol Definition * Symbols Definition * f:f:the original imagef ′:the image received by the watermark detector. f(i):i th pixel of fZ:Z:the size of the image f f M (i):the seven most significant bits of f(i) f l (i):the least significant bit of f(i) w:w:generated binary watermark of the same size M as the image f w(i):the i th bit of w w ′:the extracted binary watermark by the decoder w ′ (i):the i th bit of w ′ k:k:the length of dependency neighborhood. L:L:the size of the neighborhood, L= k × k. S(i):the secret non- deterministic dependency information of pixel i calculated N(i):the square dependency neighborhood centered at pixel i consisting of k × k pixels including pixel i itself D:D:the binary difference map between w and w ′ with its i th pixel denoted as D(i) (D(i)  {0, 255}) indicating whether w(i) and w ′ (i) are different. link

Part 2 – WM Scheme – Embedding Algorithm * Embedding Algorithm * 1. Generate w with the secret key shared with the detector. 2. For each pixel i in image f A. Calculate the secret dependency S(i) according to B. Adjust f l (i) so that the following equation holds (1) where  denotes the (XOR) operation. (2) linkBACK

Part 2 – WM Scheme – Detection Algorithm * Detection Algorithm * 1.Generate w with the secret key shared with the embedder. 2. For each pixel i a.Calculate the secret dependency S(i) from the received image f ′ according to Eq (1) b. Extract the watermark bit w ′ (i) according to: c. Calculate D(i) between w(i) & w'(i) using: (3) (4) link

Part 2 – WM Scheme – Experiment on Attack * Experiment on Attack * 1. Low-pass filtering attack. Example of common signal processing 2. Geometric attack. 3. Forgery attack. 4. VQ attack.

Part 2 – WM Scheme – Experiment on Attack- Low Pass * Low-Pass Filter Attack * a.Watermarked image. b.difference map after the watermarked image is low pass filtered.

Part 2 – WM Scheme – Experiment on Attack- Geometry * Geometry Attack * a.The cropped image. b. The difference map showing the cropped trace.

Part 2 – WM Scheme – Experiment on Attack- Forgery * Forgery Attack * a.The tampered image. b. The actual region tampered. c.The difference map with k=9 d.The difference map with k=7 LINK

Part 2 – WM Scheme – Experiment on Attack- VQ * VQ Attack * a.The image lena. b. The image with LSB and second LSB flipped. c.The image with the LSB plane flipped. d.The image with the second LSB plane flipped.

Part 2 – WM Scheme – Experiment on Attack- VQ * VQ Attack * continued a.The patched image. b. The difference map.

Summary * Summary *  Overview of the watermarking system (fragile watermarking)  Spatial watermarking scheme that can detect large range of attacks.  The discussed scheme has been extended to allow adding info. in more bits (2 and 3 bits)  high capacity + less quality

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