High capacity reversible data hiding and content protection for radiographic images

The watermarking of digital images has an important role in the protection of digital content with respect to many aspects. In this paper we present a reversible watermarking algorithm for hiding information into medical images having luminance histograms with particular characteristics. Some radiographic images have the property that not all the gray levels are present; this leads to sequences of 0 values (0-runs) in the corresponding histograms. It is possible to use these 0-runs to encode information by modifying pixels having gray levels contiguous to these runs; by encoding also the run information it is possible to restore the original image after extracting the stored data. In this work we present a novel reversible watermarking technique capable of exploiting all the 0-runs in the image histogram to achieve high capacity. We show that an optimization problem arises for those cases in which two or more non-zero frequency gray levels are contiguous to 0-runs. Part of the watermark information may be devoted to a digital signature of the original image, whose authenticity may also be verified by a user.