| abstract |
The invention is a document security system characterized by a data substrate having photographic or printed information on a base print, and also having a personalized polarization-altering overlay sealed to the base print and encoded with additional coded information readable under the influence of a polarizing viewer. The low-security information, such as name, social security, account number and photograph, are printed on a card to form the base print. Additional information of greater security, which may be a bar code or alphanumeric characters, is imprinted in the polarization-altering overlay by an appropriate physical process, such as radiation exposure or thermal, chemical or mechanical treatment, which optically modifies localized regions of the overlay. Tampering with the card, which will require removing and physically modifying the overlay, altering the base print information, and resealing the overlay, will create optical errors which become evident when the tampered document is viewed through the polarizing viewer. The invention provides an security document system with tamper-resistant and tamper-evident features that are easy to detect and difficult to imitate, the document also being long-lasting and cost-effective to produce and use. The invention is applicable to identification documents such as drivers' licenses, passports and immigration cards, and also to monetary instruments such as credit cards, stock and bond certificates, and currency notes. |