Patent ID: 7976068

Claim:
A print medium containing an invisible security image comprising: a printed substrate, a first pattern of line elements forming a latent image printed on the substrate in an invisible ink that is rendered visible when illuminated by light containing a non-visible wavelength, a second pattern of line elements forming a visually integrated setting for the latent image printed on the substrate in an invisible ink that is rendered visible when illuminated by the light containing the non-visible wavelength, the first and second patterns differing from each other but being not readily distinguishable to an unaided eye when illuminated by the light containing the non-visible wavelength, and a third pattern of line elements printed on the substrate in a visible ink, wherein at least one of the first and second patterns of line elements overlaps the third pattern of line elements, and wherein the overlapping patterns of line elements in visible and non-invisible ink are arranged so that when illuminated by the light containing the non-visible wavelength, any interference effects are substantially indistinguishable between the latent image formed by the first pattern and its visually integrated setting formed by the second pattern, and wherein the interference between the overlapping patterns occurs at moiré frequencies that are not readily discernible.