Self-recovery Fragile Watermarking Algorithm For Image Content Authentication

This paper firstly describes the research background,significance and application of digital image watermarking technology,and introduces the basic framework,common attack types and quantitative evaluation index of self-recovery image fragile watermarking algorithm.The second chapter analyzes the self-recovery image fragile watermarking algorithm from the aspects of watermark generation,watermark embedding,tamper detection and tamper recovery,and summarizes the problems of the existing algorithms.Two self-recovery image fragile watermarking algorithms are designed to solve these problems.In order to improve the tamper detection performance and restoration image quality,a multi-level tamper detection and double restoration image watermarking algorithm is designed.5 bits recovery watermark is generated based on block of size 2�2 pixels,and 5 bits authentication watermark and 7 bits recovery watermark are generated based on block of size 4�4 pixels.The authentication watermark is embedded in itself,and two types of recovery watermark are embedded in different mapping image block based on different secret key.In the tamper detection process,the algorithm shows better tamper detection performance by using authentication watermark and two types of recovery watermark.When there is a synchronization tampered block,extracted recovery watermark from block of size 4�4 pixels restores synchronization tampered block.Experimental results show that the watermark embedding capacity of the designed algorithm is 2bpp,the watermarked image quality is about 44.1dB,which ensures good invisibility;the multi-level detection improves the tamper detection performance,and two types of recovery watermark increase the chance of restoring tampered image.Compared with the existing five-bit mean algorithm,the scheme to restore the image quality has also been improved.To take watermark embedding capacity and restoration image quality into account,a variable capacity self-recovery image watermarking algorithm is designed based on SVD(Singular Value Decomposition)and DCT(Discrete Cosine Transform).4 bits authentication watermark is generated based on SVD with block of size 4�4 pixels and authentication watermark is embedded in itself.The DCT coefficients are obtained by quantizing DCT with block of size 4x4 pixels.Calculating the DCT coefficient range and the proportion by a large number of experiments,and the DCT coefficients are coded by the appropriate length coding bits.The texture structure of the image block is determined according to the DCT coefficients and a variable-length recovery watermark is generated based on DCT coefficients�10 bits recovery watermark for a texture block and 6 bits recovery watermark for a smooth block.Recovery watermark is embedded in mapping image block based on the secret key.The validity of block is determined by comparing the extracted and reconstructed authentication watermark and recovery watermark;a tampered texture block is restored with 10 bits recovery watermark and a tampered smooth block is restored with 6 bits recovery watermark.Experimental results show that the embedding watermarking capacity of the designed scheme is 1.75?2.75bpp,and the watermarked image quality is about 41dB,which can effectively resist the general tampering,collage attack and constant-average attack,and can locate the tampered area accurately and restore the tampered image.Finally,a MATLAB simulation system is designed,and the self-recovery image fragile watermarking algorithm is tested and verified by the simulation system.