Digital Watermarking Technology And Its Application Research

Digital watermarking, which has been proposed as a solution to the problem of copyright protection for multimedia data, is a process of embedding messages invisibly into media data by making small modifications to them. The messages could be copyright information or secret messages. And they should have a very little influence on host media, hence invisible to illegal receivers.In this thesis, the common robustness strategies, based on various watermarking schemes referred in research papers, are formulated; some robustness ones against geometrical transforms are investigated; the fair evaluation of digital watermarking schemes is researched deeply; and a communication-model-based digital watermarking scheme is proposed. In the communication-model-based digital watermarking scheme, the method of message encoding is applied so to enhance its robustness and to express watermark message more efficiently.The main goal of digital watermarking research is achieving high robustness against a variety of possible attacks. Although many robust watermarking schemes have been proposed, common theories under them are rarely researched. This thesis investigates most robust schemes, and then presents common robustness strategies: spread spectrum, embedding redundantly, etc.Possible attacks on still images cover JPEG compressions, image filters, and geographical transforms. While researches on how to achieve robustness against JPEG compressions and image filters has been carried out extensively, researches against geographical transforms has been rarely done. This thesis investigates three possible solutions: invariant solution, template solution, and auto-correlation solution.In recent years a variety of watermarking schemes has been proposed, but each one has its own evaluation criteria, which makes it difficult for its users to compare qualities among them. So research on the evaluation of watermarking scheme has become indispensable. This thesis has researched the foundation of the evaluation of watermarking scheme, and the application of StirMark benchmark to the evaluation of watermarking scheme.Watermarking schemes referred in papers are most O-bit ones. This thesis proposes a communication-model-based watermarking scheme, which embeds multi-bit watermark message into host-media once at a time. In this scheme, the method of message encoding is applied, which expresses watermark message efficiently and enhances the robustness of watermarking system.