An improved copy-proof document is disclosed having a cancellation phrase with an alternating dot pattern which enhances both the detail rendition and protection of such documents. The method of making such a document by preprinting the cancellation phrase in a single tone pattern of alternating dot...http://www.google.de/patents/US4351547?utm_source=gb-gplus-sharePatent US4351547 - Security document and method for making same using an alternating dot pattern
