US Patent 7906198 Document containing security images

A document containing security images which enable original documents to be distinguished from copies of the originals. The document 60 bears an image 63 containing a latent image 68. Latent image 68 may be formed from two or more images 65 and 66. The first image 65 is preferably formed at a high line frequency and at a first angle in one or more colors. The second image 66 is preferably formed at a lower line frequency at the same angle as first image 65 and in one or more colors. The colors in the first image 65 and the second image 66 are preferably chosen so that latent image 68 has substantially the same color as image 63.