Research And Application Of Semi-Fragile Digital Watermark Based On Transform Domain

The digital medium has the characteristic being able to be revised effortlessly, duplicating and spreading in Network Era, the protection of digital medium becoming extremely urgent. The fragile watermark, as an effective implement in the integrity authentication for multimedia, has become an active and flouring research topic. For the sake of saving the network bandwidth and storing resource, the image is usually compressed; semi-fragile watermark which can fight against legal operation arises at the historic moment, and a need of not only localizing the tempered areas accurately but also recovering the tempered areas. Besides, there is a need of changing the digital image holding a watermark into to material object image holding a watermark in a lot of application. Therefore, recovering the tempered areas and the material object watermark are arousing more and more people.The paper mostly studies the application of the semi-fragile digital watermark in multi-media content authentication. It firstly studies the technology of watermark producing, watermark embedding and watermark detecting. It analyzes current semi-fragile watermark algorithms from the view of content authentication, combines DCT, DWT compress standard, human visual system characteristic and image geometry moment invariability in space transformation and chaotic system, designs two kinds of effective semi-fragile watermarks system, and bringing forward one kind of material object watermark. The main working content as follows:Firstly, the paper explores and analyzes the semi-fragile digital watermark techniques, and expounds of researching background and meaning. Furthermore, it analyzes and compares the typical semi-fragile watermarking algorithms. These works lay a foundation for my further job.Secondly, it studies the DCT technology, the image geometry transformation characteristic and the image geometry moment, and proposes a semi-fragile watermark algorithm which is robust to geometry transformation attack, and applies the algorithm to the license authentication to authenticate car license, the main difficult point among them are: robust to print attack , robust to scan attack , and robust to the geometry transformation attack. These are researched and simulated.Study Human Visual System, DWT coefficient characteristic and Image Processing Algorithm finally, analysises the semi-fragile digital watermark in application, proposes a semi-fragile watermark which can not only detect tempered areas accurately but also restore tempered areas clearly. Apply this algorithm to electronic police system to solve the problem when the photograph content produced by the electronic police system accepts suspicion.