Research And Application On Watermark-based Image Authentication Algorithms

With the development of networks, multimedia information has greatly enriched.At the same time the protection of multimedia, especially for image, has become animportant issue. In order to judge the accuracy and integrity of the images,authentication techniques have been developed accordingly. Image authenticationtechnologies fall into two categories, which are signature-based image authenticationand watermark-based image authentication. Signature-based image authenticationtechnologies require additional signature information, on the contrary,watermark-based image authentication technologies embed watermark in the originalimage with no need of additional information. Therefore, watermark-based method isgenerally common used in image authentication area.This paper's main contributions are to study three watermark image authenticationalgorithms, and to make improvement in different aspects.1. Image authentication based on fragile watermark. In the realization of imageauthentication, it can detect all type of image operations. Image authenticationalgorithms link watermark bit value and the value of gray-scale together through amapping function. In the embedding process we adjust the pixel value, in order tomap it to the corresponding value of the desired watermark bit. Any pixel valuechanges will be reflected on the extracted watermark bit.Thus we can detect andlocalize the tampered area. But the algorithm exits some security flaws. Animproved algorithm is presented to overcome the security problem, and it can beapplied to the digital camera image authentication.2. Image authentication based on the semi-fragile watermarking. In someapplications we need to distinguish the type of operation. The authenticationsystem can tolerate the goodwill operations, such as JPEG compression operation,but not other malicious operations, such as crop and substitution. Imagecompression is a common image processing operation that generally be acceptedas goodwill operations. This paper proposes an authentication algorithm than can accept JPEG compression operation, but refuse the other illegal operations such asreplace and Shear.3. Image authentication combined with copyright protection. Some authenticationalgorithms combine two applications that are image authentication and copyrightprotection together. Our algorithm makes use of different color channels of RGBcolor space to embed different types of watermarks for different purposes,However if the embedded copyright information amount is too small, thealgorithm's application can be quite limited. Therefore, an improved algorithm isproposed to embed more bits of watermark. In the extracting process of copyrightinformation the image authentication results can be used to optimize the result ofcopyright information extraction.