A Semi-fragile Watermarking Algorithm for Copyright Protection and Tamper Localization of Engineering Graphics

Current watermarking algorithms for CAD engineering graphics do not consider the characteristics of graphic primitives and the obvious disadvantage of these techniques is that they are severely weakened by low transparency,poor robustness and inaccurate tamper localization.This paper proposes an effective semi-fragile watermarking algorithm for CAD engineering graphics.Firstly,the watermark sequence is circularly extended.Then,the watermark is successively embedded into a scale factor of the adjacent graphic primitive.Watermark extraction is an inverse process of watermark embedding and the correct watermark information can be obtained from the extracted watermark sequence by statistical analysis.Comparing the extracted watermark sequence with the theoretical embedding values,the integrity of the graphics can be verified and the modified part can be located accurately.The experimental results show that the proposed algorithm can not only be immune to translation,rotation and scaling operations,but also resist modification,deletion and addition of primitives and other malicious attacks with high robustness,while tampering localization can be achieved precisely by using this algorithm.