Single-color screen patterns for copy protection

A copy-protection system for verifiable documents comprising:

• a document containing a verifiable security feature as a latent image within a visually integrated setting, the latent image and the visually integrated setting each comprising an array of print elements arranged in a pattern of spaced lines, the patterns of the latent image and the visually integrated setting configured with common colors, common print densities, and common line frequencies,
• the latent image and the visually integrated setting being substantially indistinguishable to the unaided eye but being visually contrastable for verification through a visual aid configured to provide a differing visual effect between the latent image and the visually integrated when overlaid on the document and aligned with at least one of the patterns of spaced lines in the array of print elements of the latent image or the visually integrated setting, and
• the print element patterns of the latent image and the visually integrated setting being arranged so that the latent image and the visually integrated setting digitally reproduce in an altered graphic form in which the latent image remains substantially indistinguishable from the visually integrated setting to the unaided eye and is not similarly contrastable through the visual aid as originally aligned with respect to the latent image and visually integrated setting of the document.

A verifiable document comprising:

• a latent image embedded within a visually integrated setting of the verifiable document,
• the latent image and the visually integrated setting being formed by patterns of commonly oriented print elements,
• the print element patterns of the latent image and the visually integrated setting being arranged with common colors, common print densities, and differing line frequencies, the common print densities being at least 20 percent and the differing line frequencies each being at least 175 lines per inch, and
• the line frequencies of the print element patterns of the latent image and the visually integrated setting differing by between 5 percent and 20 percent of each other.

A verifiable document comprising:

• a latent image including a first line-screen pattern formed by an array of print elements arranged as systematically spaced lines having a first color, a first print density, a first angular orientation, and a first line frequency;
• a visually integrated setting surrounding the latent image, the visually integrated setting including a second line-screen pattern formed by an array of print elements arranged as systematically spaced lines having a second color, a second print density, a second angular orientation, and a second line frequency;
• wherein the first color matches the second color and the first print density matches the second print density, such that the latent image is substantially indistinguishable from the visually integrated setting to the unaided eye;
• wherein at least one of a difference between the first and second angular orientations or a difference between the first and second line frequencies is sufficient to allow the latent image to be distinguishable from the visually integrated setting via a visual aid having a line frequency configured to generate differing interference patterns for the latent image and the visually integrated setting while the visual aid is aligned with at least one of the first or second line-screen patterns;
• and
• wherein the document is further configured such that a digitally reproduced copy of the latent image and the visually integrated setting includes print elements that fill in spaces not occupied by the first and second line-screen patterns so as to blur the differences between the latent image and the visually integrated setting so that the latent image is not similarly distinguishable from the visually integrated setting with the same visual aid.