Research Of The Semi-Fragile Digital Watermarking Algorithm Based DWT

With the popularity of Internet, using and transferring digitized media has become more and more frequency in recent years. We are enjoying the convenience and shortcut of Internet and realizing some negative impacts in transferring the digital multi-media information, but the most important problem is the copyright protection of the digital product. So the digital watermarking technique as the important branch of information security is developing on such appliance request, the copyright of digital products is protected by the technology.Developments of digital watermarking technology have been very fast, experts from home and abroad have posed a series of optimal digital watermarking algorithm. In this paper, we shall first analysis the characteristic of digital watermarking technology and present status, investigate some optimal digital watermarking algorithm both here and broad. Based the shortcoming of the present algorithm, this paper presents a new robust digital watermarking scheme and semi-fragile watermarking algorithm based DWT(Discrete Wavelet Transform).For the robust digital watermarking scheme, this paper presents the embedding and extraction technique in detail, Such new embedding and extraction arithmetic are based on modular operation. The DWT and DCT are used in the algorithm, the original image was decomposed into its high pass and low pass bands using DWT, select some bands as the watermarking embedding bands, the DCT is operated on this bands. Applying topic image processing operations to the marked image, the experiments results show that: such scheme is robust against cropping, JPEG compression and noise disturbance; As for the mean filter of 3 X 3 neighborhood and rotation, the extracted watermark is not intact; As for the resizing image, firstly reduce the image, then magnify the image, the extracted watermark is not good.For the semi-fragile digital watermarking scheme, this paper introduces the embedding and the authentication technique in detail. The embedding algorithm draw on the thought of "cocktail of watermarking", the double watermarks are embedded into the original image, the two watermarks play complementary roles in resisting various kinds of attacks, the value of two watermarks are drawn from the same watermark sequence in this paper, the difference is that they are embedded using two different modulation rules: positive modulation and negative modulation. Applying topic image processing operations to the marked image, the experiments results show that: such scheme is robust against JPEG compression and noise disturbance. The authentication of tampered is operated by the tampered evaluation function. The value of tampered evaluation function is zero when the attacks are not operated. The bigger the value, the more extent of tampered. the experiments results show that: as for the cropping and adding other image into the watermarked image, the region of tampered is localized accurately, but as for the cropping region displaced by other image, the authentication of tampered is not accuracy.