Research On Image Watermarking Algorithm For Content Authentication And Copyright Protection

With the rapid development of computer network and multimedia techniques, digital multimedia applications have been widely used in many areas. The development of digital technology not only brings convenience to people, but also makes us involved with troubles of information security, including illegal copying, forgery, tampering, etc. Thus how to protect multimedia data from violation has become an important issue in information security field. Digital watermarking technique as an effectual method of content authentication and copyright protection has gotten the attention of scholars both at home and abroad. In this dissertation, the digital image watermarking for content authentication and copyright protection is studied in detail. The main contribution includes:(1) According to the problems of poor ability against attacks in existing reversible watermarking algorithm, a robust adaptive multifunctional watermarking algorithm is proposed. In this algorithm, the recovery watermark and authentication watermark are generated by the method of2DPCA (2Dimension Principal Component Analysis) and Hash function, respectively. According to the proposed block mapping method, the watermarks are embedded into its far mapping block adaptively. Moreover, MC (Mapping and Compensation) method is proposed to avoid overflow and underflow problems. The experimental results show that this algorithm can not only restore the original image losslessly if it has not been changed during transmission, but also can approximately recover the original image if it encounters malicious attacks during transmission. Moreover, the proposed algorithm can effectively resist collage attack and shearing attack.(2) Since existing watermarking schemes usually cannot recover the tampered region, a safe variable-capacity self-recovery watermarking scheme is proposed. Both watermark embedding capacity and security are taken into account. The original image is divided into texture blocks and smooth blocks, and according to the characteristics of different blocks, the different length compound watermarks are produced. Then the compound watermarks are embedded into the other blocks based on the new proposed scheme called three level secret-key embedding scheme (TLSES). And then detect the tamper blocks and restore them by the three level tamper detection scheme (TLTDS). The experimental results show that this algorithm can not only accurately detect the tamper region and restore image, but also can effectively resist mean attack and collage attack.(3) Since existing watermarking algorithm usually has single function, and it cannot combine quite well with imperceptibility, security and capacity, a region-adaptive semi-fragile dual watermarking scheme is proposed. The original image is divided into different regions, i.e., a robust watermark region, a fragile watermark region, and a region with no watermark. And, then, the interrelated robust and fragile watermarks are embedded into different regions by the status code and bit substitution techniques. The proposed dual watermark scheme not only has higher PSNR, better security and larger capacity, but also achieves the dual functions of copyright protection and integrity verification.(4) Since existing robust watermarking algorithm usually cannot resist various geometric attacks at the same time, a new anti-geometric attack watermarking algorithm based on the Contourlet transform is proposed. It presents the concept of "Space Direction Significant Tree (SDST)" using the Contourlet coefficients’father and son relationship at different resolutions, and determines the important factors to embed watermark information. And it adopts the improved imitation normalization method to resist geometric attacks. The algorithm not only has larger capacity and better imperceptibility, but also has good robustness to scaling, rotation, flipping and other attacks.