On some constructions of monochrome visual cryptographic schemes

Most of the secret sharing schemes are based on algebraic calculations in their realizations. But there are some different realizations of the secret sharing schemes. Visual cryptography is one such secret sharing scheme. In a visual cryptographic scheme, for a set P of n participants, a secret image is split into n shadow images called shares, where each participant in P receives one share. Certain qualified subsets of participants can ldquovisuallyrdquo recover the secret image with some loss of contrast, but other forbidden sets of participants have no information about the secret image. In this paper we review with appropriate examples some of the methods for the construction of monochrome visual cryptographic schemes for general as well as for threshold access structures.