Study on the parameters of the semi-fragile watermarking based on JPEG properties

As a new authentication technique for digital information, semi-fragile watermarking has gained great development, and since JPEG compression is one of the usually used image processing methods, more and more semi-fragile watermarking algorithms based on JPEG compression standard are proposed, but how to make full use of the properties of JPEG compression is still a problem. In this paper, the theory of semi-fragile watermarking based on properties of JPEG and DCT coefficients are introduced, and the parameters that affect the performances are analyzed theoretically and experimentally. The result of study shows that the positions of DCT coefficients used to generate watermark, the number of watermarks generated from a couple of blocks and the positions used to hide watermarks have great effect on the performances of the algorithm. Unless some special requirements exist, both the positions of coefficients used to generate and embed watermark should be chosen according to the order of zig-zag, and usually the best performance can be obtained when only one bit watermark is generated from a couple of blocks.