Using Correlation Marks, invisible images are hidden within a normal, visible image, such as a photograph, using specially designed halftone screens. The halftone screens used to embedded the Correlation Marks can be used like any traditional halftone screen, — no additional image processing is required.

Different from digital watermarking technology, Correlation Mark technology hides an invisible image during the printing process, No alteration to the original image data is required. And because the hidden mark is inserted during the printing process, each copy of a document can have a unique hidden image.

Hidden images made using Correlation Marks technology are not visible to the human eye. They can be detected either by scanning and processing the printed image, or by overlaying a transparency containing a ‘key’ on top of the document to reveal the hidden image. Correlation Marks are robust to copying and distortion and can be detected in reproductions of the halftone image.