Research Of Image Watermarking Against Geometrical Attacks And JPEG Compressed Domain Watermarking

With the wide use of multimedia technology in the information age, such as digital audio, image and video, it is possible to replicate, transmit, and distribute digital content that is unauthorized in an effortless way for pirates. So it is an urgent task to protect the intellectual copyright of multimedia. This problem has been effectively solved by digital watermarking technology, which has become a very active research hotspot in academic fields in recent years.As the variety of watermark and its wide use, this dissertation will focus on the technology of image digital watermarking as follows:(1) A new blind quadruple watermarking scheme of digital images against geometrical attacks has been proposed. The problem of the geometrical synchronization has been solved by means of a searching method and the polar coordinates have been used to embed the same quadruple watermarks. Experimental results show that the scheme is robust to the geometrical distortions including rotation, scaling, cropping and local distortions.(2) A fragile digital watermarking scheme for image authentication has been improved. Any alteration and modification to the watermarked image can be detected. But the watermark can be embedded only in BMP image in the original scheme, and the watermark detection will not succeed if we compress the watermarked image. However, compressing the image is inevitable for the sake of network bandwidth and storage resource. In this dissertation, the watermark has been embedded in compressed domain and the improved scheme can be used in extended field combined with compress technology.