| 摘要 |
An improved security document (10) according to the present invention includes a substrate having a surface for carrying indicia. The document has background printed matter (20), consisting of a pattern of elements of a first size and frequency, printed at a first density on the surface. The document further has a cancellation term (22), consisting of a pattern of elements of a second size and frequency, printed at a second density on the surface. Elements of one of the first size or the second size are sufficiently small such that they are not reproduced by a color copier at a particular copier setting, and elements of the other of the first size or the second size are sufficiently large such that they are reproduced by the color copier at the particular copier setting. As a result, a copy of the security document made on a color copier displays the cancellation term. At least a portion of the security document surface is divisible into a plurality of bands extending across the surface. The sizes of the elements and the density of the background printed matter and the cancellation term vary together across the bands in a direction generally normal to the bands. As an alternative, the frequencies of the elements may vary across the bands such that the density of the background printed matter and the density of the cancellation term are changed. Such a document may be printed with different colors of ink on different portions of the document, and with the bands in which a color transition occurs being printed with two colors of ink at differing screen angles. |
