Browse Prior Art Database

Document Copy Prevention

IP.com Disclosure Number: IPCOM000084387D
Original Publication Date: 1975-Nov-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 38K

Publishing Venue

IBM

Related People

Queener, CA: AUTHOR

Abstract

The IBM Technical Disclosure Bulletin, Vol. 18, No. 1, June 1975, at page 43, describes apparatus using specular paper to record not-to-be-copied copied information, such that a subsequent attempt to copy by an office copier results in little or no light being reflected to the copier's photoconductor. The apparatus described herein enhances the ability to protect such a secure document by providing two photocells which are used to measure the intensity of reflected light at two different positions, and by a comparison of the ratio of these two light intensities.

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Document Copy Prevention

The IBM Technical Disclosure Bulletin, Vol. 18, No. 1, June 1975, at page 43, describes apparatus using specular paper to record not-to-be-copied copied information, such that a subsequent attempt to copy by an office copier results in little or no light being reflected to the copier's photoconductor. The apparatus described herein enhances the ability to protect such a secure document by providing two photocells which are used to measure the intensity of reflected light at two different positions, and by a comparison of the ratio of these two light intensities.

In Fig. 1 a normal nonspecular original document 10 is positioned on the copier's document glass and is line scanned by an incoming light footprint 11 from the copier's illumination source, not shown. Two photocells 12 and 13 quantitatively measure the light reflected from the original document at different angles 14 and 15 measured from the normal to the document glass. The resulting light reflection pattern can be qualitatively characterized by closed curve
16. The bump 17 in the curve is caused by the specular reflection from the underside of the document glass.

The normal original document approximates a Lambertian or totally diffuse reflector, wherein the reflected illumination intensity is given by the equation I=I(omicron) cos theta, where I(omicron) is the reflected intensity at the normal to the document glass, and the angle theta is angles 14 and 15. Thus, if angle 18 is a relatively small angle, the ratio of the output of photocell 12 to the output of phot...