A new optical encoding method for security applications is
proposed. The encoded image (encrypted into the security products) is
merely a random phase image statistically and randomly generated by a
random number generator using a computer, which contains no information
from the reference pattern (stored for verification) or the frequency
plane filter (a phase-only function for decoding). The phase function in
the frequency plane is obtained using a modified phase retrieval algorithm.
The proposed method uses two phase-only functions (images) at
both the input and frequency planes of the optical processor leading to
maximum optical efficiency. Computer simulation shows that the proposed
method is robust for optical security applications.