Image Watermarking Attacks And Countermeasures

Digital watermark is a novel and effective method for copyright protection. It becomes a hot spot in multimedia information security research. Watermark is also a core branch of hiding technology research. Many experts have done lots of research on the watermark and there have been many research paper on it. However, The robust watermark that for the oriented-copyright protection still remains to be a very difficult research area. Currently, there isn't an algorithm can completely resist all the attackers. This thesis does some research on the attack method of the current image digital watermark and provides the corresponding strategy. Finally, based on these countermeasures, we propose a novel defendable watermark model, which provides a mature model system for the digital watermark.The thesis first gives an overview of the image digital watermark techniques, presents all kinds of classical watermark algorithms and the disadvantages in those algorithms. Then, it pays emphasis on some digital watermark attack methods, and analysis the procedure of the specific attack method and the algorithms of attacked watermark. Based on that analysis, it integrates the corresponding countermeasures for those attacks. Finally, it proposes a full watermark structure for copyright protection. And introduces the authentication centre (CA) for allocation and conservation of the secret key. The authentication centre uses a time-stamp, which proves the watermark embedded time and resists the interpretation attack effectively. At the same time, a trusted third party (TTP) is introduced to the open watermark, which brings out a feasible standard watermark model for the author, user and the authentication. And itanalyses the resist ability of the model in theory.A perfect watermark structure is required to implement the digital work's copyrightprotection. The method that introducing the asymmetric secret key system in the watermark structure can improve the resistant ability; the double watermark algorithm is used to meet the requirement of the original image copyright protection and rewriteprotection. Though the algorithm provided in that model hasn't been implemented. The way that use double watermark technique, and use asymmetric secret key system and a different secret key during watermark checking gives a novel idea to people: different information can be embedded into the image according to different requirement and provided for multiple utilization, because fragile watermark only require the trusted third part to extract and the user is transparent. The robust watermark required the authentication centre to extract the watermark. At the same time, the zero knowledge proof for the author ID can be done by the authentication centre, which is the idea of the cryptology authentication and can solve problem of the copyright ownership more effectively.