Watermarking scheme for tampering detection in remote sensing images using variable size tiling and DWT

In this paper, a semi-fragile watermarking scheme specifically developed for remote sensing images is presented. The method can be tuned to embed the mark depending on the content and the signature to be protected. The suggested method is based on tiling the original three-dimensional images into blocks of different sizes according to the relevance of the area to protect (bigger blocks are used for less relevant areas). For each of these blocks, the discrete Wavelet transform (DWT) is applied to each selected spectral band and the obtained LL DWT sub-bands are used to build a Tree-Structured Vector Quantization tree. This tree is then modified using an iterative algorithm until it satisfies some criterion. Once the target value is reached, the marked block is obtained using the new LL DWT sub-band together with the other original sub-bands (LH, HL and HH) of the block. A secret key produces a different criterion for each block in order to avoid copy-and-replace attacks. The use of the LL DWT sub-band for each spectral band makes it possible to obtain robustness against near-lossless compression attacks and, at the same time, relatively strong modifications are detected as tampering.