Research Of Watermarking Scheme On Still Image

Digital watermarking was recently proposed as a new mean to provide copyright protection of multimedia data and image authentication .It is a research hot spot in multimedia information security domain. Watermark is also a core branch of hiding technology research. Many experts have done lots of research on the watermark and gained some achievement. The robust watermark for the oriented-copyright protection still remains to be a very difficult problem. Currently, there isn't an algorithm that can resist all attacks.Discrete Cosine Transform is the key technique in the subsistent signal source compression coding Standard JPEG.A majority of energy of a image is distributed on middle-frequence AC coefficients and DC coefficients which shows human vision is sensitive to changes on low-frequence coefficients of DCT. And the high- frequence coefficients of DCT will be mostly affected during image compressing, so watermark signal will be embedded on the middle-frequence coefficients of DCT. Visual model is to model HVS using mathematics method. The value of JND can be calculated accurately by making use of vision characters in vision model, so accordingly embedded location and intensity can be decided appropriately in order to solve the conflict between the robustness and imperception.On the basis of discussing systematically the application of digital watermarking in still images, a robust watermark scheme based on HVS and DCT is given. This scheme is originated from QIM, and it's a blind scheme. The result of the experiment shows that this scheme is robust to compression, noise and shearing. At the same time, this scheme is expanded to the field on color images. In this paper, the frail watermark is also discussed at some degree .The scheme on the frail watermark by using HASH function MD5 is testified by a simple experiment . At last, the problem about the attacks and security of watermark is discussed in detail.