Cryptography General Question:

Naor and Shamir developed what they called visual secret sharing schemes, which are an interesting visual variant of the ordinary secret sharing schemes.

Roughly speaking, the problem can be formulated as follows: There is a secret picture to be shared among n participants. The picture is divided into n transparencies (shares) such that if any m transparencies are placed together, the picture becomes visible, but if fewer than m transparencies are placed together, nothing can be seen. Such a scheme is constructed by viewing the secret picture as a set of black and white pixels and handling each pixel separately. See for more details. The schemes are perfectly secure and easily implemented without any cryptographic computation. A further improvement allows each transparency (share) to be an innocent picture (e.g. a picture of a landscape or a picture of a building), thus concealing the fact that secret sharing is taking place.