Browse Prior Art Database

COUNTERFEIT DETECTION METHOD

IP.com Disclosure Number: IPCOM000027240D
Original Publication Date: 1995-Dec-31
Included in the Prior Art Database: 2004-Apr-07
Document File: 2 page(s) / 139K

Publishing Venue

Xerox Disclosure Journal

Abstract

Position modulation of line screens are used to add hidden or obscured messages to a photocopy. This modulation can be small enough so as not to be easily detected with the unaided eye, but is made clearly visible when the photocopy is examined with a transparent analyzer. The analyzer can be inexpensive to produce and distribute and thus provide for easy field detection of the hidden message. This does not prevent the copying of any document, but does allow the easy detection of any document that has been so copied. An identification of the user, copier location and time could even be included in the obscured message. Multiple generation copies would contain messages from each of the copiers used.

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XEROX DISCLOSURE JOURNAL

COUNTERFEIT DETECTION METHOD
Richard H. Tuhro

Proposed Classification
U.S. C1.355/046 Int. C1. G03b 27/44

Position modulation of line screens are used to add hidden or obscured messages to a photocopy. This modulation can be small enough so as not to be easily detected with the unaided eye, but is made clearly visible when the photocopy is examined with a transparent analyzer. The analyzer can be inexpensive to produce and distribute and thus provide for easy field detection of the hidden message. This does not prevent the copying of any document, but does allow the easy detection of any document that has been so copied. An identification of the user, copier location and time could even be included in the obscured message. Multiple generation copies would contain messages from each of the copiers used.

Commercially available color copiers can produce excellent quality copies. The copies are so good that they can be a source of counterfeit legal or financial documents. The ideal anti-counterfeit device on a copier might cause no noticeable degradation in the copy quality, yet allow the easily detection of a copied document anywhere detection was needed without or with inexpensive detection devices. Tagging copies with special toners or tiny glyphs can provide a solution, but these solutions have a detection problem, and may require additional printer hardware. If they are made small enough to be invisible to the unaided eye, they can stress the capability of the printer. The present approach can be implemented with minimal added printer hardware, can be easily detected with an inexpensive detector, and although they are tiny effects, they can be easily printed even if below the printer resolution because they produce the image with a statistical effect that is integrated by the eye over a larger area.

In a normal color copy, a pictorial screen is printed on the copy, the line or dot width is modulated from zero to fill in, thus producing the desired variations in the density of the copy corresponding to the density of the original. This process is repeated in each of the color print primaries, producing a full color copy. To encode the hidden message, the line or dot screen is displaced a small amount, for example, an amount that could be below the visible detectability level and below the pixel level. This modulation can be changed in two dimensions and extend over the entire copy area...