Study On Semi-Fragile Watermarking Based On Digital Image

Along with the fast development of the multi-media technology and computer network, more and more digital products are being transmitted through the internet. While bringing great convenience to people's life, it also cause illegal copy and malicious tempering. Under this circumstance, the digital watermarking technology are being widely applied to protect multi-media products, especially used as a solution for digital image authentication.Digital watermarking is the technology to protect digital products and to maintain data safety. It's an important branch of information hiding technology. Image authentication based on digital watermarking has different advantages from digital signature, so is the hotspot in the spot of information authentication.In this paper, a branch of authentication watermarking, semi-fragile watermarking is studied. The background, principal and basic frame is dissertated, and the algorithms of existing semi-fragile watermarking system are discussed, on their advantages and disadvantages. Some basic principals of digital image processing, which is related to watermarking, are also described, and the paper discussed the most widely used digital image format, JPEG, on how it works, and how to combine watermarking technology with JPEG format image.Then the paper proposed a new semi-fragile watermarking method. The watermarking method is used on JPEG(Joint Photographic Expert Group) images, which is the most widely used format of compressed image. The paper proposed a new image-characteristic extraction method based on HVS(Human Visual System) and the image specification. In the embedding process, the embedding type and embedding location is detailed discussed and proposed an optimized embedding method. Both theory analysis and experiments show that the method has a lower degration effect on images compared with the SARI system, which is proposed by Ching-Yung Lin and Shih-Fu Chang, while at the same time has lower false-alarm rate and the miss rate is almost the same as SARI. The paper also studied the application of semi-fragile watermarking and gives some opinions, containing consideration on the semi-fragile watermarking evaluation standards. Digital watermarking technique is inspired by application requirements, and the article also take prospect on the future of the area.