Empirical evaluation of a JPEG2000 standard-based robust watermarking scheme

In this paper an empirical evaluation of the lossy compression properties of the JPEG2000 standard for watermarking purposes is performed. The JPEG2000 standard is used as a basic tool for determining both how and where the embedded watermark should be placed in the image. The original image is slightly modified in order to generate a similar image (indistinguishable by the observer), and the mark is embedded in the pixels presenting differences between both images. Previous experiments show that the properties of the resulting watermarking scheme depend strongly on the transformation stage characteristics of the lossy image compression system. Several parameters related to the JPEG2000 standard are tested, in addition to the compression ratio: the wavelet transform, block size, and the number of levels of decomposition for each block. These parameters affect not only the capacity but also the robustness of the watermarking scheme: the number of different pixels between the original image and the slightly modified one, and the distribution of such differences. For evaluation purposes we use the Stirmark benchmark. We compare the impact on system performance of each one of the JPEG2000 standard parameters, for several kinds of attacks, namely filtering (including sharpening), JPEG lossy compression, cropping, row and column removal, and a combination of rotation, cropping and scaling.