Analysis of the “Wavelet Tree Quantization” watermarking strategy and a modified robust scheme

Here we study a recently proposed watermarking scheme based on the paper “Wavelet Tree Quantization” (WTQ) by Wang and Lin (IEEE Trans Image Process 13(2):154–165, 2004). In given scheme, wavelet coefficients corresponding to the same spatial locations are grouped together. Two such groups, selected at random, constitute a supertree. Some of these supertrees are quantized to embed the watermark information in the image. In the process of cryptanalysis we first identify the groups which are quantized during the watermark insertion process. Then we select the non-quantized groups and quantize them too, to remove the watermark. Experimental results show that the watermark is completely removed by this attack. The cryptanalysis falls under the cipher text only jamming attack which requires only a single watermarked copy. Further, we suitably modify the WTQ scheme to make it robust against such cryptanalytic attacks.This is an extended and revised version of the paper Cryptanalysis of “Wavelet Tree Quantization” Watermarking Scheme presented at the International Workshop on Distributed Computing, IWDC 2004, Kolkata, 27–30 December 2004, Lecture Notes in Computer Science, vol. 3326, pp. 219–230. Springer, Berlin Heidelberg New York (2004). Section 4 of this paper introduces a modified scheme which is an addition over the conference version. Part of this work has been done while the author T. K. Das was visiting Indian Statistical Institute, Kolkata during 2004.