Visual cryptography based watermarking: definition and meaning

The proliferation of digital data, and their distribution over different kinds of communication channels are making the copyright protection a very important issue in the digital world. Watermarking techniques and visual cryptographic schemes have been recently used in different approaches for the copyright protection of digital images. Watermarking is generally used to embed “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 try to provide a general model for the watermarking schemes obtained from the combination with visual cryptography. Furthermore we discuss some possible extensions of the combined approach taking into account different visual cryptographic schemes where multiple participants are involved and their possible applications in new scenarios