Correlation Marks

Correlation Marks provide a unique and simple method to protect and track documents. Based in digital screening technology, Correlation Marks take advantage of spatial correlations in halftone screens to create a self-authenticating, secure document containing an invisible, hidden image.

Technology Description

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.


  • Self-authenticating
  • Compatible with traditional halftoning and printing processes
  • Original image data preserved
  • Each document copy can have a unique hidden image
  • Robust to copying for document tracking


  • Product Fraud – protection against counterfeiting
  • Negotiable Documents – currency, tickets, coupons, checks
  • Identification and Authentication – ID’s, licenses, certificates
  • Sensitive Documents and Contracts – financial, legal, health care
  • Protecting ownership rights of an image
  • Authenticating an image to show it has not been altered
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Intellectual Property Summary

Xerox Intellectual Property includes patents, patent applications, and know-how.

For your convenience and review, we have provided a sample of selected patents from our portfolio.

U.S. 7706025 Moire-based auto-stereoscopic watermarks
U.S. 7352879 Conjugate cluster screens for embedding digital watermarks into printed halftone documents
U.S. 7006256 Watermarked image generator and method of embedding watermarks into an input image
U.S. 6731409 System and method for generating color digital watermarks using conjugate halftone screens
U.S. 6263086 Automatic detection and retrieval of embedded invisible digital watermarks from halftone images
U.S. 6252971 Digital watermarking using phase-shifted stoclustic screens

For Licensing Information

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