Visual cryptography based watermarking

The combination of watermarking schemes with visual cryptography has been recently used for the copyright protection of digital images. The derived schemes try to satisfy the increasing need for the security of multimedia data, caused in turn by the enormous amount of digital information that is daily created and distributed over different kinds of communication channels. Watermarking is generally used to insert “secret” information into an original image, with different purposes and different features, usually as a means to assess the ownership of the modified image. Visual cryptography refers to a way to decompose a secret image into shares and distribute them to a number of participants, so that only legitimate subsets of participants can reconstruct the original image by combining their shares. The combination of both techniques can provide some important solutions for tampering verification and the resolution of disputes on the ownership of a given image, as provided by several proposals appeared in literature. In this work we present a general model for the watermarking schemes obtained from the combination with visual cryptography Furthermore we discuss also the improved robustness such schemes can achieve, trying to analyze the effects that random or induced errors can have on the reconstructed watermark. Finally, some possible extensions of the combined approach are also introduced considering different visual cryptographic schemes and their possible applications in new scenarios.