Abstract: A system and method for providing a security check on a credit card. The credit card has first data recorded thereon in the form of optical gratings to provide for card uniqueness and second data recorded thereon in a magnetic track also located on the card. The optical gratings on the card cannot be reproduced by "skimming" or without destroying the card itself. When the magnetic track is recorded by a bank issuing the card, some reference to the first data on the card is included and encrypted on the magnetic track by the bank's encrypting hardware so as to eliminate fraudulent duplication or use of the card. The first data, which is unique to the card, is compared with selected portions of the encrypted second data to provide a security check to determine the validity of the card being used. The optical gratings are embossed on an aluminized plastic strip which is sandwiched between plastic sheets in the credit card to form a non-separable and tamperproof card structure.

Abstract: An optical identification system including a reader for reading superimposed optical gratings on a record medium in which the reader has a grating plane and a radiant energy source for directing energy therefrom along an optical axis to the grating plane. Detectors are positioned in the reader to receive diffracted beams from the optical gratings on a record medium positioned at the grating plane. The reader also includes an optical imaging system having a concave lens for directing a zero order reflected beam which is displaced from the optical axis back to the grating plane to enable the resulting beams diffracted from the optical gratings to be received at the detectors whenever a record medium is displaced slightly from the grating plane.