Research On Redundant Digital Watermarking Techniques

The digital media has become a main way for information communication along with the wide use of network. At the time, multimedia information security problems includes copyrights piracy emerged as side effects of the popularity of the digital representation and distribution over network. Digital watermarking technology provides novel ways to solve these security problems for multimedia information.In this dissertation, we study the technologies of digital watermarking and propose a blind image watermarking algorithm based on Discrete Cosine Transformation ( DCT ), which operates in the frequency domain, embeds watermark in a selected set of DCT coefficients. After embedding, the watermark is adapted to the image by exploiting the masking characteristics of the human visual system, thus ensuring the watermark invisibility. It improves therobustness of watermarking by embedding redundant watermark with coefficient K. It is prone to be compatible with JPEG and MPEG standard. The experiments show that our algorithm is more robust than irredundant watermarking algorithm. We also propose a novel detector aiming at the limitation of common detector, which adopts the variable standardization and makes it more reasonable to select the detecting threshold. At the same time we discuss the analysis and design of the watermarking application system and focus our discussion on a watermarking protocol based on the semi-trusted third party and its implementation.