发明授权
US4227720A Protected document 失效
受保护的文件

Protected document
摘要:
Disclosed is a protected document such as a negotiable instrument, a title instrument, identification document or other documents which should be kept secure from illegal copying by color copiers. The method of making the document comprising preprinting a "VOID" or other warning or cancellation phrase pattern in half tone or multitone on the document and camouflaging this pattern is also disclosed.
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