Security code marking for documents, uses moire patterns in printed spots of concentric circles which can be scanned to reveal code

摘要

The security marking (1) is a pattern of concentric circles, which are slightly distorted by the data which is to be encoded, producing a watered silk or moire pattern. As the documents move past a scanner, two areas (2, 3) of the marking are scanned and the images are combined on a projection surface (11), to reveal a digitized image (12) of the security message or other marking.