| 摘要 |
COPY-INVALIDATING DOCUMENT The text discloses for use in printing valuable documents an allover pattern of warning indicia which is merged by human sensory perception with its background but is distinguished and reproduced by xerographic copying as a result of the employment of two different screen values for the indicia and the background which are respectively within and beyond the reproductive capability of the copier machine when used in the stated context. Adjunctively, document validating indicia are also printable on such documents in a screen value beyond the reproductive capability of xerographic copiers at the lighter settings at which the lesser screen value used for said warning indicia or background will reproduce.
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