ABSTRACT
This chapter discusses the various categories of visual cryptography, explores the need, advantages and disadvantages of each category of visual cryptography, and identifies the research gaps in various dimensions of visual cryptography. Visual Cryptography schemes are broadly classified into three categories viz. Traditional Visual Cryptography (TVC), Extended Visual Cryptography (EVC) and Dynamic Visual Cryptography (DVC). TVC were based on binary secret images. Binary and halftone images both consist of only two intensities, one is for black and other is for white. Halftone images are more appropriate for visual cryptography in comparison to thresholded binary images because of their randomness. Many methods exist in the literature to convert a multitone/continuous tone image into a halftone image. Randomness of the shares increases the vulnerability for cryptanalysis and may create confusion in share identification in case of a large number of participants.
