Comparative evaluation of semifragile watermarking algorithms

Semifragile watermarking techniques aim to prevent tampering and fraudulent use of modified images. A semifragile watermark monitors the integrity of the content of the image but not its numerical representation. Therefore, the watermark is designed so that the integrity is proven if the content of the image has not been tampered with, despite some mild processing on the image. However, if parts of the image are replaced with the wrong key or are heavily processed, the watermark information should indicate evidence of forgery. We compare the performance of eight semifragile watermarking algorithms in terms of their miss probability under forgery attack, and in terms of false alarm probability under nonmalicious signal processing operations that preserve the content and quality of the image. We propose desiderata for semifragile watermarking algorithms and indicate the promising algorithms among existing ones. (C) 2004 SPIE and IST.