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Abstract

A method and article for optically encoding copies of a printed document to make the copies unreadable to a casual observer uses a mask having alternating transparent and opaque, white-colored areas placed over the document prior to making a first photocopy of the document, referred to as a first coded half. The opaque regions of the mask, which preferably are spatially periodic, obscure portions of printed letters to make the first coded half unreadable. The mask is then shifted in location relative to the document so as to position transparent regions of the mask over formerly obscured areas, and vice versa. A second photocopy, or second coded half is then made. The first and second coded halves are then physically transmitted or telefaxed to a recipient, who must superimpose the first and second coded halves to render the document readable.

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First Claim