Study On Digital Image Watermarking Technique

With the rapid advance of Internet, digital media has become a main way to information dissemination. People can acquire a wide range of multimedia data through Internet easily. While at the same time, many multimedia information security problems emerge as side effects of the above convenience, including illegal copying, forgery, tampering, etc. Thus how to protect multimedia data from violation has become an important issue in information security field. As a main application of information hiding technique to multimedia copyright protection, the digital watermarking technique has been proposed as a viable solution to the copyright protection and authentication of multimedia data in a networked environment since it makes it possible to identify the author, owner, distributor or authorized consumer of multimedia data. So in recent years it has drawn extensive attention and has been widely applied. Digital watermarking is a popular technique, which involves communication and information technology, image and speech processing, signal detection and evaluation, mathematics, human audio and visual systems, computer network and application, etc. Digital watermarking, which embeds some invisible information—watermark—into the original multimedia data such as image, audio, video signals, etc., can authenticate the ownership or integrality of these multimedia data so as to protect the copyright. The hidden messages could be copyright information or other secret messages. Generally it demands robustness and imperceptibility. This paper addresses the digital image watermarking technique. First, an overall review is made on the digital watermarking technique, including its definition, background, basic principle, characteristics, general system structure and main application fields of digital watermarking. Second, based on the previous work and current research situations, a new image-adaptive watermarking scheme in DCT domain is proposed by incorporating DCT, HVS models, image scrambling and quantization modulation such as dither modulation, so that the binary image watermark can be embedded into the multimedia image adaptively. In order to enhance the robustness of the algorithm, the scrambled watermark is embedded in the direct components and perceptually significant components by utilizing the feature of masking of HVS. The watermark can be recovered from the watermarked image without any knowledge of the original image. Next, in order to test the imperceptibility and robustness of the algorithm, simulation experiments are conducted. Experimental results indicate that the watermark generated with this algorithm is both invisible and robust to the common signal processing attacks such as cropping, JPEG compression, noise contamination, etc. Finally, the technique of digital watermarking based on DWT is discussed by comparing a typical watermarking algorithm in DWT domain with that in DCT domain.