Research On Digital Image Watermarking Technique

In the last few years, multimedia systems have gained more and more popularity due to the ever increasing amount of information that is stored and transmitted digitally. The large diffusion of digital multimedia documents, due to several advantages of digital media with respect to the traditional ones, has, however, a limiting factor, represented by the case of reproducing or transmitting digital data in their exact original form without admit to the owners, which encourages copyright violation. A possible solution consists of digital watermarking, a new technology based on concept belonging to many research areas, such as steganography, cryptogtaphy, communication theory and signal processing. A digital watermark is a signal permanently embedded into digital data (such as audio, images, video, text) that can be detected or extracted when it is needed to make an assertion about the data. The watermark should be hidden in the host data in such a way that it is inseparable from them, and it can resist to many operations not degrading the host document. In chapter 1, this new technology is presented in detail. In this paper image watermarking technique is analyzed and the main contribution consists of as followings:1. A new digital watermarking technique is proposed based on discrete wavelet transform. In order to enhance the robustness of watermark, watermark was based on the content of the original image. Pesudorandom permutation, division and spectrum spread techniques were used to improve the robustness of watermark. Different from the traditional techniques, in our method, watermarks were embedded for two times, the holistic watermark was embedded first and then was divided watermark, and watermark here was embedded both into the low part of the wavelet transform of the image but also to the high parts. The extraction process extracted both the holistic watermark and the divided watermark in turn. The watermark based on the content of the original image and the watermarks that given beforehand were compared in the same condition and the experimental results showed that this kind of watermark has a...