| 摘要 |
A document containing security images which enable original documents to be distinguished from copies of the originals. The document 60 bears an image 6 3 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 second image is preferably formed between the lines, dot, swirls, or spots of the first image and may be printed eithe r in register or out of register. 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. If the document 60 is reproduced, the reproduced copy is preferably very distorted, such as containing moiré patterns, and also contains the latent image 68, the composite image of the first image and the second image, preferably appears in the reproduced copy. A document may be authenticated as an original document by detecting the presence of a predetermined hidden security image and/or by determining the layout of the document to be the same as the expected layout of an original document. |
