Patent ID: 8211490

Claim:
A method for including a double layer security mark in digital document data defining an image of a document to be printed, said method comprising: defining a fluorescence mark region including a fluorescence mark in said digital document data, said fluorescence mark region defined by first colorant mixture data for defining a first colorant combination and second colorant mixture data defining a second colorant combination, wherein said first and second colorant combinations are a metameric pair that define respective first and second colors that are at least substantially indistinguishable in visible light and wherein said first colorant mixture data and said second colorant mixture data define colorant-free areas of said fluorescence mark region; modifying said fluorescence mark region to define a double layer fluorescence mark region including said fluorescence mark and also including at least one visible light object defined by third colorant mixture data, wherein said third colorant mixture data defines a third color that varies in average color and luminance from both said first and second colors in visible light, wherein said step of modifying said fluorescence mark region includes: (i) writing said third colorant mixture data to said fluorescence mark region and protecting at least some of said colorant-free areas of said fluorescence mark region with a mask to prevent writing of said third colorant mixture data to said colorant-free areas that are protected by said mask; and, (ii) replacing at least some of said first and second colorant mixture data with said third colorant mixture data such that said fluorescence mark region includes said first, second, and third colors and said colorant-free area that are protected by said mask; and, printing a document on paper using said document data including said double layer fluorescence mark region, wherein said first, second and third colors defined respectively by said first, second, and third colorant mixture data are printed, said third color and one of said first and second colors being darker or lighter than the other of said first and second colors when said printed document is viewed in UV light.