Overview of Visual Cryptographic Systems Based on XOR Function

Visual cryptography based on XOR is a science that gives solutions of several problems in relation with the security. From now on it is often used in the daily applications in relation with the computer field. Among the application cited in this article; print and scan, which used the WALSH transformation, there is also the color image application, which used the HALFTONE technique to print the image according to the model CMY. To succeed in removing the secret correctly from the recovered image; two criteria are taken into account: minimization of the pixel expansion and maximization of the contrast.