We present an optical coding technique that enhances the anticounterfeiting power of security holograms. The principles of the technique is based on the moire phenomenon. The code in the hologram has a phase pattern that is invisible and cannot be detected by optical equipment, so that imitation is extremely difficult. Holographic, photographic and embossing technique are used in fabricating coded holograms and decoders.
Applied Optics, 1997, Vol 36, Issue 31, p. 8096-8097