Abstract: A security document with a design (e.g. a generally oval seal) is constructed in such a way that the design is full value halftone, such as produced from juxtaposed line screens having a frequency between 100-133 lines per inch. Negative and positive masks having an image (e.g. arabic numeral, letter, or other symbol), are used with the screens to produce a printing plate. A document is printed with the printing plate in a conventional lithographic process, and there is an overprinting on the design (at least that portion having the image) with a white opaque ink or overprint varnish to produce an image. The image is not readily visible to the naked human eye when viewed generally perpendicular to the plane of the document, but is readily visible by the naked human eye when the document is tilted so that it is viewed distinctly non-perpendicular to the plane of the document.

Abstract: Security paper having a number of parallel lines having a substantially uniform first spacing, irregularly interrupted by a plurality of stripes having a second spacing greater than the first spacing, is flexographically printed on at least one face of a web which becomes, after further processing, a security document such as a bank check. The parallel lines typically are substantially straight and of substantially uniform thickness and formed of flexo ink, such as the type which becomes invisible when bleached. Alphanumeric indicia are preferably provided within the stripes either oriented parallel to the parallel lines (and alternately extending from top to bottom, and bottom to top), or perpendicular to the parallel lines. A pattern is provided that repeats at an interval significantly greater than the length of the security document formed from the security paper.