Towards tamper detection and classification with robust watermarks

In this paper, we present a novel wavelet-based double watermarking system for the detection and subsequent characterisation of the tampering of images. Most tamper detection techniques use fragile watermarks. However, our previous work showed that this type of watermark is frequently completely destroyed by compression, which in many cases is undesirable. In addition, it gives little or no information about the nature of the attack. We propose using two robust watermarks, one inserted at the embedder, the other at the detector. The second watermark is used as a reference with which the first watermark may be compared. This allows additional information not previously available about the nature of the attack to be obtained. The use of a robust strategy prevents the watermark being easily destroyed, but instead allows the system to continue to perform after significant attacks.