Research On Digital Image Watermarking Algorithms Resistant To Geometric Attacks

With the rapid development of information technology and computer network in recent years, it becomes more and more convenient to store, copy and transmit the digital multimedia information. At the same time, the information security and copyright protection of digital multimedia work have become an urgent social problem. As one of the most effective methods to protect the copyright of digital multimedia, digital watermarking has become one of the research hotspots in the field of information security. The watermarked work will inevitably suffer some either intentional or accidental interferences or attacks in the course of transmission. Therefore, digital watermarking for copyright protection must have good imperceptibility, high security and strong robustness. At present, digital image watermarking systems are confronting with various attacks, among which geometric attacks are the severest threaten, and are also regarded as one of the main bottlenecks on the way to commercial application of digital image watermarking techniques. Most of existing algorithms resisting to geometric attacks usually focus on the problem of global and linear attacks, but few are resistant to challenging cropping and recently reported random bending attacks (RBAs). Consequently, achieving robustness against various geometric attacks (including cropping and RBAs) will be of great significance.In my dissertation, still images are taken as main research object. First, existing image watermarking algorithms resisting to geometric attacks are summarized and analyzed thoroughly. By utilizing the theory of image processing and characteristic of digital watermarking system and researching on the influence of various geometric attacks on digital image features, some image features robust to geometric distortion are acquired. Then, by comprehensive application of cryptography, chaotic scrambling and spread spectrum communication technology etc, three blind image watermarking algorithms robust to geometric attacks are proposed. The focal point of this dissertation is summarized as follow:(1) The research status of digital image watermarking resistant to geometric attacks is summarized, and existing image watermarking algorithms resisting to geometric attacks are classified and analyzed on performance deeply.(2) By utilizing the invariant property of the statistical characteristics of an image during geometric transformations, an effective color image watermarking scheme robust to geometric attacks based on histogram modification is presented.(3) On the basis of researching on the affine covariance of the extend centroids of an image and the geometric invariance of singular values of an image, a geometric attacks resistant image watermarking algorithm based on extend centroids and DWT-SVD is proposed.(4) By using one of the color image geometric invariant representations—mean-based 2D color histogram and combining organically cryptography, the concept of the third part, zero-watermarking technique, a geometrically invariant color image zero-watermarking scheme using mean-based 2D color histogram is presented.