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Image analysis of photochromic ink for security applications

Photochromic materials exist in two different color states, with switching between states being achieved by irradiation, with ultra-violet and visible light. By printing patterns and data using both photochromic ink and ordinary ink, it is possible to create a document that is difficult to forge and easy to authenticate. Security is achieved only by public ignorance about and the relative rarity of photochromic materials. Very high levels of security are possible, using modern data encipherment techniques. These are so secure that no known algorithmic method exists for breaking them in a practical amount of time. It should be understood that encipherment algorithms provide a way of protecting a message. Guaranteeing the authenticity of a complete document is better achieved using photochromic materials. This article describes a scheme which employs both techniques to achieve higher overall security than either can provide individually. Central to this idea is the ability to sense the presence of photochromic materials using machines, prior to recognizing specified patterns and reading text.