COPY PROTECTION OF MULTI-COLOUR DOCUMENTS

摘要

A security document printed in colour is provided with a security area intended to defeat copying on a dot-image type colour copier. Such area comprises a line pattern printed in a dark neutral colour on a light neutral colour and is such that colour copying creates a multi-coloured noire pattern not present in the original. The line pattern may include areas of rulings which differ in pitch, line thickness and/or orientation. A security area in the form of a printed disc of radial tapering lines is also disclosed.