Fifth International Conference on Information and Communications Security ICICS 2003 Huhehaote City, Inner-Mongolia, China, 10-13 October, 2003 A DWT-based Digital Video Watermarking Scheme with Error Correcting Code Pat P. W. Chan and Michael R. LYU Computer Science and Engineering Department The Chinese University of Hong Kong

Outline Introduction New Video Watermarking Algorithm Experimental Results Future Direction Conclusion

Watermarking Algorithm Introduction Watermarking is a concept of embedding a special pattern, watermark, into a document. Watermarking is a key process for the protection of copyright ownership of electronic data. In this presentation, we will focus on the video watermarking scheme. Watermarking Algorithm Watermarked Image Ì Stego-Image I Watermark W Secret / public key K

Introduction Video watermarking is challenging Video watermarking introduces some issues not present in image watermarking. Due to large amounts of data and inherent redundancy between frames, video signals are highly susceptible to pirate attacks, including frame averaging, frame dropping, frame swapping, statistical analysis, etc. However, the currently proposed algorithms do not solve these problems effectively. Existing techniques are not aware of the usefulness of the audio channel in a video.

Introduction A new scheme for robust blind digital video watermarking with error correcting code will be introduced. The features of the video watermarking algorithm are: Our scheme embeds different parts of a single watermark into different scenes of a video under the wavelet domain; To increase robustness of the scheme, the watermark is refined by the error correcting code, while the correcting code is embedded as watermark in the audio channel; Our video watermarking algorithm is robust against the attacks of frame dropping, averaging and statistical analysis; It allows blind retrieval of embedded watermark which does not need the original video; The watermark is perceptually invisible. To tackle these problems. we’ve proposed a new scheme for robust blind digital video watermarking with error correcting code.

Watermarking Scheme Overview

Video Preprocess: DWT & Scene Change Detection Video frames are transformed to wavelet domain. Perform scene change detection. Each scene is embedded with the same watermark, so it can prevent attackers from removing the watermark by frame dropping. Different watermarks used for successive different scene can prevent attackers from colluding with frames from completely different scenes. Mark with m1 Mark with m3 Mark with m7 Mark with m0 Scene change occur

Watermark Preprocess Scale the watermark to a particular size with the following equations 2n ≦m , n>0 p + q = n , p and q > 0 Size of image = 64˙2p X 64˙2q Divide the image into 2n small images with size 64 X 64 m -- # of scene change of the video Different frames using different watermarks can make the watermarks resistant to attacks by frame averaging Hard to reconstruct the watermark without knowledge m=10, n=3, p=1, q=2

Watermark Preprocess Encrypted watermark m’0 Original watermark Preprocessed watermark m0-m7

Video Watermark Embedding Exchange C[i] with max(C[i], C[i+1], C[i+2], C[i+3], C[i+4]) while W[j] = 1 Exchange C[i] with min(C[i], C[i+1], C[i+2], C[i+3], C[i+4]) while W[j] = 0 LL, HH coefficients are not watermarked

Audio Watermark Error correcting code is extracted from the watermark image Embedded in audio channel as an audio watermark This watermark can provided the error correction and detection capability for the video watermark Average

Audio Watermark Embedding Spread-Spectrum Watermarking Modulated Complex Lapped Transform (MCLT)

Watermarked Frame & Wave Original video frame and wave Watermarked video frame and wave

Watermark Detection Video is split into video stream and audio stream. Watermarks are extracted separately by audio watermark extraction and video watermark extraction. Then the extracted watermark undergoes refining process

Video Watermark Detection if WC[i] > median(WC[i], WC[i+1],WC[i+2], WC[i+3], WC[i+4]) W[j] = 1 else W[j] = 0 Original video frame Watermarked video frame Extracted Watermark Recovered Watermark

Watermark Refining Error correcting codes are extracted from the audio stream The video watermark extracted is refined by this information with the following equation k = kth block of the average image i = x-coordinate of video watermark j = y-coordinate of video watermark T = Threshold that the pixel need to correct P: Q = the ratio of importance of extracted watermark to the average

Experimental Setup VirtualDub -- a video capture/processing utility (http://www.virtualdub.org/) A video clip with 1526 frames of size 352 X 288 Experiments: Experiment with Frame Dropping Experiment with Frame Averaging and Statistical Analysis Experiment with Lossy Compression Experiment with Cropping Watermarked Frame Measurement:

Experiment with Frame Dropping As a video contains a large amount of redundancies between frames, it may suffer attacks by frame dropping. From the experiment, we found that our scheme achieves better performance than the DWT-based scheme without scene-based watermarks.

Experiment with Frame Averaging and Statistical Analysis Frame averaging and statistical analysis is another common attack to the video watermark. When attackers collect a number of watermarked frames, they can estimate the watermark by statistical averaging and remove it from the watermarked video Scenario of statistical averaging attack

Experiment with Frame Averaging and Statistical Analysis The watermarked video is statistically analyzed by colluding a number of video frames and the watermarks are extracted and NC values are obtained. It is found that the proposed scheme can resist to statistical averaging quite well.

Experiment with Lossy Compression The performance of the scheme is significantly improved by combining with audio watermark, especially when the quality factor of MPEG is low. When the quality factor of MPEG is low, the error of the extracted watermark is increased and the watermark is damaged significantly. As the error correcting code is provided from the audio watermark, it can survive the attack by lossy compression which is applied to the video channel.

Experiment with Cropping Watermarked Frame DWT inherits many advantages in resisting the attacks on the watermarked frames. It achieves perceptual invisibility and attacks by image processing techniques. Cropping is one of the most common attack to video watermark.

Conclusion & Future Direction Video watermarking is needed since copyright protection is essential. Video watermarking is different from image watermarking. A DWT-based Digital Video Watermarking Scheme with Error Correcting Code is proposed. Use visual-audio watermark to increase the robustness of the scheme. Increase robustness of the scheme by improving the way to embed the watermark. Use better error correction coding. Make use of the information from the video, such as time information to increase the robustness of the watermark.

Q & A