A Recoverable Semi-fragile Watermarking Algorithm Based On Multi-direction Authentication

With the rapid development of information technology,the sharing and transmission of digital multimedia has become more convenient and faster.The emergence of multimedia editing tools has brought convenience for people to copy and modify digital multimedia.However,there is a problem that the digital multimedia can be easily tampered and forged without leaving obvious traces by the criminals who use these multimedia editing tools,which directly lead to the problem that the authenticity and reliability of the digital multimedia content are difficult to identify.Semi-fragile watermarking technology can not only detect the tampered area effectively,but also tolerate some conventional signal processing that does not change the main content of the carrier.Thus,it has become an important technology of digital multimedia content authentication and has developed rapidly in recent years.However,there are still some shortcomings in semi-fragile watermarking watermarking technology.For example,the accuracy of tamper detection in semi-fragile watermarking technology is quite poor and most semi-fragile watermarking algorithms can not recover the tamper effectively.In order to solve the above problems,we studies and analyzes the semi fragile watermarking technology based on image,and the main research contents are as follows:(1)In this thesis,we analyze the reasons for the poor accuracy of tamper detection in current semi fragile watermarking algorithm,and a multi-direction authentication strategy is proposed to improve the accuracy of tamper detection,which embeds different bits of feature information of every image block into multiple mapping blocks.When the tamper detection is needed,the tamper equations related to the image block and its multiple mapping blocks are firstly established,and then the tamper is located according to the relationship between the sum of the tamper equations and the judgment threshold.(2)A recoverable semi-fragile watermarking algorithm based on the multidirection authentication is proposed in this thesis,which realizes the function of recovering the tampered area on the basis of accurately locating the tampered area.The characteristic information is extracted from the maximum singular value of the image blocks in the proposed algorithm and it is scrambled by multiple directions to obtain the authentication watermark of the image blocks.In order to recover the tampered area,the recovery watermark generated from the average pixel value of the image blocks is encrypted by the chaotic sequence.The authentication watermark and the recovery watermark are embedded into the intermediate frequency subband of the image after wavelet transform by significant difference quantization.When the authenticity of the image needs to be verified,the multi-direction authentication strategy is used to detect the tamper of the image,and the recovery watermark is used to recover the tampered area.(3)The invisibility,robustness,tamper detection accuracy and quality of recovery image of the proposed algorithm are analyzed in detail through experiment in this thesis,and the results of experiment are compared with the current semi fragile watermarking algorithms.The results of experiment show that the invisibility and robustness to JPEG compression and Gaussian noise of the proposed algorithm is good.At the same time,the accuracy of tamper detection and the quality of recovery image are better than the comparison algorithms.