The Robustness Of The Watermarking Algorithm And Realization

With the rapid growth of internet communication and the development of multi- media technology, the security problem of digital media becomes the bottleneck limiting the development of information technology, digital watermark appears as an efficient means of protecting multimedia documents. Robust watermark, which is an important subclass of digital watermark, is always the focus of research. Requirement of robustness against common signal processing operations is the characteristic of robust watermark. Based on the previous work and current research , we have made the following work:(1) For robustness against JPEG compression, we analyze the invariant properties theorem during JPEG compression which was proposed in previous work, then proposed an improved scheme. Based on those work, we design a watermarking algorithm, which has robustness against JPEG compression with common quality factor. In addition, the proposed algorithm can perfectly detect the watermarks without degrading the visual quality of original image.(2) Based on the concept of watermarking as communication with side information which was proposed by Cox, we proposed a watermarking algorithm, by using the information extracted from cover image at the embedder, this watermarking strategy has achieved partial resistance to geometrical transformations and some common image processing operations. In the design of watermark encoder, through the combination of side information and watermark, our system also obtained the robustness against copy attack.(3) Effort on obtaining the resistance to print/scan are made.To solve the geometrical distortion problem appeared during the process of print/scan, two schemes were proposed. First, resistance to geometrical distortion was obtained by using moment normalization; Second ,we focus on the phase of Fourier-Mellin transform. Before detecting watermark, synchronization could be retrieved by using the phase information. To eliminate the influence of pixel value distortion generated during print/scan process, a DFT-based robust watermark algorithm was designed, which could successfully detect watermark from a severe distorted image.