ELECTRO-OPTICS  LABORATORY

Three different optical security systems are surveyed in this chapter. Their common feature is the appearance of meaningful images on the system’s output. In the first system, two phase-only transparencies are placed in a 4f correlator such that a known output image is received. In the second system, two phase-only transparencies are placed together in a joint-transform correlator for the same purposes. In both cases, the two phase masks are designed with an iterative optimization algorithm with constraints in the input and the output domains. In addition to simple verification, these security systems are capable of identifying the type of input mask according to the corresponding output image it generates. The third system is different from the two others in the sense that the system’s input signal also is a meaningful image. This last system can offer various solutions for steganography, watermarking, and information coding. This chapter summarizes research first published in [1–3].