Research On Several Robust Digital Watermarking Algorithms

With the development of Internet, the communication with multimedia information reaches an unheard-of depth and width, and the ways to issue the multimedia data become more and more diverse. But it also exposes some problems obviously: The digital contents are much easier to be pirated or tampered. So people have to pay highly attention to the way that could not only take the advantages of the Internet but also protect the digital copyrights. The digital watermarking techniques have been researched and applied widely, which are proposed to address such issues.In this paper, we introduce the background and the basic theory of digital watermarking techonology, and particularly discuss the issues about image watermarking algorithms and digial watermarking protocol.An important research on the digital watermarking techniques is the design of robust digital watermarking algorithms. In this paper, three digital image watermarking algorithms are proposed, meeting different challenges.More and more researchers focus on meaningful digital watermarks embedding, especially, the gray-scale watermarks, because they have many good advantages but are hard to deal with. First, a simple but effective chaotic encryption algorithm of image is given in this paper, and then a gray-scale blind watermarking technique operating on DCT domain is presented, which automatic embeds watermark bits by adjusting the relationship of coefficients of the selected DCT block with the mean of corresponding coefficients of DCT blocks around the selected DCT block. The experimental results show that the proposed algorithm is effective and robust to common image processing operations and some geometric distortions such as JPEG compression and cropping.Based on an optimized perceptual model of the zero tree structure, two kinds of watermarking algorithms are proposed in this paper: one embeds a watermark of Gaussian sequence, and the blind detector is based on correlation;the other embeds a watermark of binary image, and the extractor is not blind. In order to maximum embedding watermark bits, the two proposed algorithms embed watermark bits in all of the significant wavelet coefficients, including the coefficients of lowest pass sub-band, and provide a good tradeoff between the transparency and the robustness based on the perceptual model. Experiments show that both of the proposed algorithms are effective and robust against common image processing operations, especially to JPEG and wavelet compression.SVD preserves both one-way and non-symmetric properties. Based on the analysis of the first column in the orthogonal matrix of SVD, we propose a block-wise image adaptive watermarking scheme using wavelet domain SVD, embedding the watermark in the first column of the orthogonal matrices. The stability of the first column is examined to select the best pairs of the neighboring coefficients for embedding. Two thresholds are employed to control the modifications of the neighboring coefficients, which are decided by the statistical properties of the local image blocks, aiming at achieving an optimaltradeoff between the transparency and robustness. Experiments show that the proposed scheme is effective and robust to common image processing manipulations, especially to JPEG compression.With the ceaseless advances in the digital watermarking techniques, how to manage digital copyrights using the existed digital watermarking techniques, namely, how to realize a secure and efficient digital watermarking protocol, becomes a research hotspot.Based on the existed watermarking protocols, we analyze the structure of the watermarking protocol, and discuss the shortcoming of these protocols as well as issue the key problems on applying such watermarking protocols. Take the advantage of the commutative encryption, the proposed buyer-seller watermarking protocol is secure and fair to both sides in digital copyright protection. The transaction is well performed between the buyer and the seller, there is no need for additional watermark authority and trust requirements. Both the buyer and the seller have no idea about final watermark contents, but the public authority has enough evidences to judge rightfully. And the buyer is anonymous in the transaction by using a pseudonym, so his privacy is well protected.