Research On Critical Techniques Of Digital Watermarking And Its Applications

Digital watermarking has been given more attention by academic and industrial society as an effective technique for copyright protection and authentication of mutimedia information along with the use of broad band network and the distribution of mutimedia information in the network. By far the field of digital watermarking has well developed, but some aspects of watermarking are neglected. In the dissertation we try to survey current techniques of digital watermarking and study the effect which brought by ECC(Error Correction Code) in the watermarking channel. At last based on the results of former parts, general steps which guide to design a watermarking scheme for a specific application have been presented and we have designed two practical watermarking sytems, i.e., CDMA-based video watermarking scheme and image-feature-based robust watermarking scheme for authentication.First, We compare SS(Spread Spectrum) watermarking technique with side-information watermarking technique in robustness, channel capacity and distortion through information theory and experiments results. Principles about the SS watermarking technique and the side-information watermarking technique are illustrated, and channel capacity and the probabity of error of these two typies watermarking techniques are given. Two typical watermarking schemes which utilize these two techniques respectively have been designed and implemented. The experiments show that embedding distortion of side-information watermarking is reduced and capacity is increased on account of exploitation of original cover, on the other hand, the SS watermarking scheme is robust for some methods of signal processing and can control probabity of error by adjusting the length of the chip sequence and the energy of the sequence.The dissertation has given results of performance enhancement which is brought by ECC, i.e, BCH code, Reed-Solomon code, Trellis code and Turbo code in the SS watermarking channel and the side-information watermarking channel. Many experiments show the ECC methods can enhence reliability obviously in watermarking channel of low error probabity. The watermarking information which can be embedded in per sample is decreased. The experiments also show that the MPSNR value using ECC is the same as the situation which does not using ECC almost.We present general steps which guide to design watermarking schemes for a specific application analysising the requirements of spceific watermarking application and the possible attacks, based on the specialties of the two typical watermarking techniques and ECC performace in the two typical watermarking channels. When we design a watermarking scheme for a specificapplication, we can grasp the main aspects regarding as standardization process. These general steps display relationships among requirements of watermarking application, possible attacks, choises of watermarking strategies and use of ECC methods.A new watermarking scheme for video based on CDMA(Code Division Multiple Access) has been designed and given the description of the algorithms and emperiments results. The video watermarking scheme can be used in the application of broadcast monitoring. An image-feature-based robust watermarking scheme for authentication has been designed, which is different from the fragile watermarking technique for authentication. The embedding operations modify original cover slightly because of the use of side-information watermarking technique. The scheme can detect whether the image is tampered or not, and also locate the modified position if tampered. The image-feature-based robust watermarking scheme for authentication can be applied in the situation of image authentication.