Steganographic printing and verification system uses transparent overlay with apparently random pattern placed on apparently random printed pattern to make picture or text visible

摘要

Coded information on packaging may be printed in monochrome with an apparently random raster pattern giving a grey field. An initial printed region (1) may have an L-shape and a small square defining corners of the printed region and the coded message may be printed in the space between the L-shape and small square. A frequency or stochastic modulation system may be used. A transparent overlay with a frequency or stochastic modulation pattern is used to visualize the coded information as a black-and-white pattern. An offset or flexographic printing process may be used.