A review paper on various visual cryptography schemes

Visual cryptography is special type of technique for encipher the confidential visual information (e.g. printed text, handwritten notes, and picture) in such a way, that decipher can be performed by an authorized user with the help of human visual system (HVS) without any complex process. It also provides high security, so that hackers cannot observe any clues about a secret image from individual cover images. There are various measures on which performance of visual cryptography scheme depends, such as pixel expansion, contrast, security, accuracy, computational complexity, share generated is meaningful or meaningless, type of secret images (either binary, gray or color) and number of secret images (either single or multiple) encrypted by the scheme. Intent of this paper is on study and performance analysis of the visual cryptography schemes and also a comparative analysis on various visual cryptography schemes.