The Research Of Digital Watermark In Static Image

The Internet and communication technology are developing quickly and digital media including image, digital audio date, and digital video is widely used. It brings some problems such as information security, copyright protection and authentification. These problems are becoming more and more urgent. Traditional encryption can protect digital data while it is in transfer. But they can't be protected any longer if they are decrypted. And sometimes the encrypted data might attract some people to decrypt them. Digital watermark technology is an efficient complementary method. It is a new technology than can protect the copyright and authenticate the origination. Digital watermark technology is attracting more and more researchers and is becoming a hot point in multimedia and signal processing domain.This paper discusses digital watermark technology in image used in copyright protection and gives two new watermarking algorithms DCT domain and DWT domain. Watermark can be inserted in spatial and transformational domain. Previous work showed that watermark in spatial is not robust. So we insert watermark data in transformational domain. The basic watermark casting method is inserting watermark into some coefficients chosen with HVS(human visual system) and characters of the original image. The watermark data can be pseudorandom sequence and binary image etc. The watermarking algorithms given in this paper insert pseudorandom sequence in DCT domain and binary image in DWT domain. In the algorithm based in DCT, we split the original image into 8*8 blocks, then do discrete cosine transform of these 8*8 blocks. We embed pseudorandom sequence into the median coefficients. We choose the median coefficients because low-spectrum part of the DCT coefficients include most of the energy of the image and human's eyes are sensitive to the low-spectrum part. What's more, the high-spectrum part of the DCT coefficients is changed a lot in compression. Experimental results show that the DCT-based watermarking algorithm can provide excellent protection under various attacks. Inserting watermark in DWT domain uses the similar inserting principle with that in DCT-based algorithm. In this paper, we embed a 32*32 binary image into median-spectrum part of DWT coefficients. The channel coding principle in communication is used in this method. Experimental results show that the method given in this paper is more robust than previous similar method.