ABSTRACT
The key property used to construct visual cryptography schemes for black and white images is the following: if we superpose transparencies with black and white pixels, the resulting pixel that our eyes see is black if at least one of the superposed pixels is black and is white if all the superposed pixels are white. Such a property can be rephrased as follows: the possible ”state” for the pixels can be represented with a bit, using 0 for white and 1 for black, and the human visual systems performs an OR of the input pixels in order to reconstruct the secret pixels.
