Digital watermarking in wavelet domain with predistortion for authenticity verification and localization

We present a blind fragile authentication algorithm by modifying a robust algorithm. The embedding process modifies the relative position of one wavelet coefficient from a vector of 3 coefficients. The introduced distortion of the watermarking system is reduced by a content dependent quantization parameter. This parameter refines the quantization step according to the magnitude of the coefficients in the vector. The smallest wavelet coefficients in the smooth areas of the image are pre-distorted to improve the performance and efficiency of the algorithm in these areas. This pre-distortion does not visually degrade the image as the introduced high frequency noise is evenly distributed over these areas. A dichotomous detector compares the extracted and embedded watermark on a bit by bit basis. This results in a high detection resolution, which can deliver information about the shape of the modified object. Embedding of the watermark with a larger redundancy increases the robustness of the system to additive white Gaussian noise attack. A weighted estimation then extracts the embedded watermark. This technique is fully described in the paper. Experimental results of this system embedded in the wavelet domain illustrate the performance and effectiveness compared with other reported fragile watermarking methods