1. A method as implemented on an encoding device for hiding within a visible representation of a first pattern, at least one second pattern, the method comprising the steps of. (i) selecting a predetermined key function; (ii) utilizing said key function to create a binary halftone representation of the first pattern, in which the first pattern is visible and the at least one second pattern is hidden, each cell in said binary halftone representation having halftone dots' position distribution corresponding to gray-level distribution of the at least one second pattern, thereby enabling processing of said binary halftone representation by a two-dimensional spatial correlator based on the key function to extract data representative of the at least one second hidden pattern.