Some Studies On The Digital Watermark Attacks Technology

With the development of computer technology and the popularity of computer network, the phenomenon that digital image was unauthorized tampering, copy and piracy is become quite common. Under the circumstances, digital watermarking has been widely development as a new way of copyright protection. Currently, many commercial watermark software products for images have emerged on the market. Attacks against watermarking systems are a direct assessment method to test whether schemes are robust or not. So it is necessary for us to study the kinds of attacks against watermarking, as the study of attack methods could promote stronger watermarking technology development.In this paper, the basic theory of digital watermarking technology and some typical image watermarking schemes are introduced, analyzed and concluded firstly. Then the watermarking attacks schemes are made a deep study, and categorized into the first generation watermark attacks and the second generation watermark attacks based on the quality of image after attacked. Lastly by studying the existing commercial watermark software on the market, the remove attack and copy attack are presented through analyzing the principle of watermark. The remove attack and copy attack are the second generation watermark attacks which have good image quality after watermark attacks.The following are some main researches in the thesis:(1) Based on studying foreign well-known watermark software, a watermark removal attack algorithm is proposed. The algorithm firstly analyzes the spatial domain and frequency domain characteristics of original images and watermarked images, and uses the prior knowledge of typical image watermarking schemes to estimate the algorithm of the watermark software. Secondly, the watermarking is estimated by using the frequency domain characteristics of watermarked images. Lastly, the watermarked image subtracts the estimated watermark amplified by a gain factor. This approach can successfully remove watermarks and ensure the quality of image. Experimental results show the scheme is effective.(2) Based on studying domestic well-known watermark software, a watermark removal attack algorithm and a copy attack algorithm are proposed. The chapter is divided into two parts. In part one, the paper analyzes the spatial domain and frequency domain characteristics of original images and watermarked images, and uses the strategy of the watermarking embedded simulation to estimate the algorithm of the watermark software, that is:first add yellow borders to the original images, then separately process R, G,B components of color images:segment the images into blocks with16*16size, and take discrete cosine transform (DCT) to every sub-block. Finally, embed watermarking to images through modifying the intermediate frequency coefficients of sub-block. In part two, under the algorithm theory of the watermark software, the watermark removal attack algorithm and the copy attack algorithm are proposed. Experimental results show that the attack algorithms are effective and easy to implement.Finally, all the work has been done in the thesis are summarizes, and some further research directions are presented.