Watermarking Algorithm For JPEG Image Authentication And Recovery

With the rapid development of modern communication, information processing and computer technology, image processing, storage and transmission are involved more and more deeply in our daily life. After image information is converted into a digital signal through sampling, quantization and coding processing, a huge amount of data bring a lot of inconvenience for storage and network transmission of data. Therefore the compression and coding become a major trend in image processing. JPEG image has been widely used with good image quality, as well as a high compression rate. Editing, modifying and other tampering of image become very easy, so the authentication of JPEG image content and the recovery of tampered area become the urgent problem.The JPEG image is as the study object in this thesis. The research status of image authentication watermarking and recovery watermarking are reviewed. Combined with JPEG compression standards, the authentication watermark information is generated by extracting unique features and embedded into the original image. And the recovery watermark is generated by extracting the important compression information of image and embedded into the original image. If the image has been tampered, the tampered area of image will be recovered by extracting the recovery watermark and reconstructing image information. Image authentication is mainly to detect whether the image is tampered and where is tampered, and the recovery watermark is to recover the tampered region of image and the recovery image can provide the basis for inferring the intention of tampering. The research purpose of the thesis is to improve the accuracy of detecting and the quality of the recovery image in ensuring the quality of the watermarked image. The research achievements are about the semi-fragile watermark of the authentication and recovery based on JPEG images. The main work is as follows:(1) A JPEG image authentication algorithm is designed based on the DC component of DCT coefficient block and the standard of JPEG compression. The DC component of DCT coefficient block is robust to JPEG compression and is fragile to tampering the contents of image. According to this feature, the authentication watermark is generated. First, the quantized DCT coefficients are obtained by decoding the original JPEG image, and then the authentication watermark is generated base on the DC component of quantified DCT coefficient block. Finally, in order to improve the performance of tamper detection, the authentication information is embedded the different regions repeatedly.(2) A JPEG semi-fragile recovery watermarking algorithm based on the difference modulation is proposed according to the characteristics of JPEG images. The embedding capacity of watermark is small because the redundant data is less, but the amount of recovery watermark is large, so the data compression of recovery watermark become a main problem. The watermark is generated through decoding the original image to obtain DCT coefficients, re-quantizing coefficients to be protected and modulating by difference. The amount of watermark is greatly reduced by using the difference modulation. Because the quantization steps of the middle and low frequency coefficients are smaller than high frequency coefficients, the generated watermark is embedded into the middle and low frequency coefficients of other image blocks to improve the imperceptibility. At the same time the recovery watermark is used to authenticate the image content. If the reconstructed watermark is different from the extracted one, the image is judged to be tampered and the recovery watermark is extracted to recover the tampered area. The experiments are conducted for the quality of the watermarked image and reconstructed image by the recovery watermark, the tamper detection performance and quality of recovery image. The experimental results are also given in detailes.