Research And Application Of Digital Image Watermark Technology

The multimedia information security problems including copyrights piracy emerged as side effects over network. In this dissertation, I study the technology of digital watermarking embedded in gray images. The main contributions of this dissertation are:An Improved Self-Adaptive Oblivious Watermark Algorithm based on DCT.Generally, the traditional watermark embedding strategy has its limitation corresponding to non-adaptive embedment model. Embed watermark with different intensity according to the types of each Discrete Cosine Tansformed block. Same watermark will be inserted several times in different parts of the image. Finally, recover the watermark by computing the even value after drawing each hiding bits with different weights from different places. The algorithm showed high accuracy.A Novel Freaquency Domain plus Space Domain Oblivious Image Watermarking Algorithm will be proposed next. A Test Serial was also embedded with the watermark into the images to highten the algorithm's accurary. In different Discrete Wavelet Transformaed sub-images repeated embedding the watermark to keep robustness. For the sake of the algorithm merged both the merits of frequency domain and space domain, so it will be robust to the filtering attacks and the Noise attacks, be cost-efficient as well. The above two algorithms would be capable of keeping the balance of the algorithm's robustness and transparency.A Watermarking Algorithm against Rotation Attacks. It's very hard to trace the original watermark's position after even minor angle rotation happened to the image with watermarks, because on this occasion the watermarking extracting process will lose the synchronism. Proposed the watermark sectors based on Discrete Wavelet Transformation and calaulate the rotation angle by Hough Tranformation to relocate the sectors' new positions. From the blocks' even values extracted the watermark successfully. The algorithm realized watermark's synchronism, accurate location, resist to minor angle attacks, common noise, image Compressing and enhancement attacks.An Practical Information Hiding Application was proposed, which added robust blind digital watermarks switched from text medical record in grey medical images.