Abstract A security device for use on identification cards, monetary documents, and the like using a reference pattern and a message pattern each having the appearance of a random pattern of dots. The reference pattern is a dense pattern of randomly positioned dots, and the message pattern is a modulated version of the reference pattern in which the dots of the reference pattern are slightly repositioned by an amount depending on the grey value or color value of a message image at each dot location. The message image is decrypted and becomes visible with a range of grey values when it is viewed through a film transparency of the reference pattern. The dot pattern may be printed, embossed or recorded as a photograph or a hologram. Decryption of the message image may be accomplished by viewing through a contact mask, superposition of images of the message pattern and reference pattern, by viewing the message pattern through a mask positioned at a real image of the reference pattern, or like means.
An anticounterfeiting security method comprising: means for extracting information from a document to use as a kernel for generating a pseudorandom reference dot pattern, means for generating a pseudorandom reference dot pattern from said kernel, means for modulating said reference dot pattern as an encrypted message dot pattern to encrypt a message and means for applying said message dot pattern to said document in an optically detectable form.
Claim 2
Dependent Claim
68 words
An anticounterfeiting security method comprising: means for extracting information from a document to use as a kernel for generating a pseudorandom reference dot pattern, means for generating a pseudorandom reference dot pattern from said kernel, means for modulating said reference dot pattern as an encrypted message dot pattern to encrypt a message and means for applying said message dot pattern to said document in an optically detectable form.
Claim 3
Dependent Claim
31 words
The method of claim 1, further comprising means for reading said message dot pattern and means for comparing said message dot pattern to said reference dot pattern, thereby decoding said message.
Claim 4
Dependent Claim
21 words
The method of claim 2, said comparing being accomplished by illuminating said message pattern with light corresponding to said reference pattern.