There is provided a non-transitory computer-readable storage medium tangibly embodying machine-readable visual representation of data encoded therein, the data being retrievable by reading and decoding the visual representation by a visual code reader, the visual representation including: multiple function patterns; a first visual code comprising a first encoded message embedded therein, and a first subset of the function patterns, such that reading the first encoded message requires reading the first function patterns subset; and a second visual code comprising a second encoded message embedded therein, and a second subset of the function patterns, such that reading the second encoded message requires reading the second function patterns set, wherein the first function patterns subset and the second function patterns subset have at least one common function pattern, and wherein at least a part of the second visual code is read differently by the reader before and after a physical event occurs.