Information Hiding Technology Based On Digital Watermarking

As present information security technology has some shortages in copyright and content protection, digital watermarking comes forth and becomes an attractive research area in information technology. This paper summarizes the evolution of watermarking technology as well as its theoretical frame, and then studies the copyright protection of still images. Two watermarking algorithms are proposed here: spread spectrum watermarking for color image based on wavelet tree structure and a blind watermarking with strong robustness based on relationship and quantization.Color images and videos are widely used in reality. Therefore, study of watermarking for color images has an important practical significance. As Discrete Wavelet Transform (DWT) has a number of advantages, study on watermarking in DWT domain becomes a trend. The first algorithm proposed in this paper, by using the spread spectrum technic, distributes the information of one watermark bit into several frequency sub-bands belonging to one wavelet tree. Such an approach improves the robustness of watermark against different attacks. At the same time, a new extracting strategy is proposed in the algorithm, which somewhat removes the salt-and-pepper noise from the extracted watermark image caused by attacks to the watermarked image and further improves the robustness. Experimental results show that the algorithm is very robust to image processing attacks such as JPEG compression, Gaussian noise, filtering, cropping and contrast enhancement.The blind watermarking algorithms without referring the original host image in the watermark extraction procedure are more useful for various applications where host images are not available. Therefore, research on blind watermarking extraction seems to be very attractive. The second algorithm takes use of blocking Discrete Cosine Transform (DCT) and blocking DWT. Its embedding method includes relationship embedding and quantization embedding. Due to the fact that both the magnitudes of coefficients concerned in the relationship indicate the block image's energy, they have the same change trend when the image is attacked. That means the relationship will be quite stable. In addition, dither modulation is used in quantization embedding, by which the tradeoff between transparency and robustness of watermarking can be easily adjusted. Simulation results show that the algorithm is fairly robust against the general image processing and it maintains satisfying transparency.