Research On Robust Digital Watermarking Techniques For Images

As the development of computer network and multimedia technology, multimedia data(such as image, sound and video) has gradually become an important source of information. So, how to ensure the security of multimedia information has become a hot research topic internationally. The traditional encryption technologies can only ensure the safety of the information during the transmittal without a efficient way to control the safety of information after it is encoded. So the traditional encryption technologies are unable to prevent the pirate from illegally copying or spreading the information. As an efficient way of solving the above problems, Digital Watermark technology emerged. In Digital Watermark technology, some special information will be embedded in the protected works to confirm the ownership and integrity which can protect the digital works from being pirated and tampered. As the compensation of traditional encryption, Digital Watermark technology is researched and applied widely in the protecting the copyright and integrity of multimedia information.Based on an overall understanding of Digital Watermark technology, this paper mainly discusses the robustness of Digital Image Watermark technology. This paper analyzes the feature of Digital Watermark and the factors that affect its robustness. For static image files, this paper provides two Digital Watermark solutions based on transform domain.The key point of Robust Digital Watermark is the ability against geometric attacks. Digital Watermark using Discrete Fourier Transform (DFT) can effectively withstand geometric attacks, so this paper put forward a DFT Digital Watermark solution based on Template Matching. In this solution, the template was added to image signals to strengthen the ability against rotating and scale transformation. The outcome of this algorithm has been verified by experiments.In image processing, lossy compression threatens the survival of Digital Watermark, so in the process of embedding or extracting, we must seek the best robustness by using the features of lossy compression. At present, the latest image compression standard—JPEG (Joint Photographic Expert Group) 2000 uses wavelet transform, compared with other transform, Image Watermark based on wavelet transform has many good features suitable for Image Watermark. Accordingly, this paper provide an embedded algorithm in discrete wavelet transform (DWT) domain based on bit replacement, this algorithm uses binary image with special meaning as the watermark information and preprocess it, in which technologies such as image scrambling, DWT and bit replacement are combined. Finally, various simulated attack was done to this watermark algorithm and the outcome proves that this solution can withstand common JPEG compressions and is useful in protecting copyright.