Abstract

A form of visual jam resistant coding is presented. Using Visual BBC, a modified form of BBC (Baird, Bahn, Collins) coding, it is shown that several images can be printed on clear plastic, such that when they are superimposed (i.e. a bitwise OR of the pixels is performed), the resulting image may look random, but the original images can still be recovered without any information about the original pictures, and without any secret. BBC is a complex subject to understand, and so Visual BBC aids the teaching of how BBC coding works, by giving students a concrete, physical model. Examples are shown, illustrating that it is possible for legitimate BBC codewords to actually look like recognizable images, rather than just random binary strings. This allows us to superimpose arbitrary pictures and separate them again in linear time without using any keys or channels specific to each picture. This is not possible in any other coding systems, such as error correcting codes, superimposed codes, or steganography systems. In addition, a number of analysis problems are described that can be given to students, which are motivated by the issues arising in Visual BBC, and which further increase student understanding of the system.

Citations