| 摘要 |
<p>A photocopy resistant article, useful, for example, in the preparation of share certificates, bond certificates, paper money, etc. is disclosed. Two adjacent areas of the surface of the photocopy resistant article appear visually continuous to the unaided normal human eye. However, one of the areas, known as the signalling area, comprises a plurality of spaced lines having an element frequency along a notional selected line which is within the resolution capability of the photocopy machine but substantially beyond the resolution capability of the normal unaided human eye. The second of the two adjacent areas, referred to as the comparison area, comprises a plurality of spaced lines having an element frequency along a selected notional line substantially beyond the resolution capability of the unaided normal human eye and of the photocopy machine. Both areas have approximately equal area occupancy ratios and the signalling area has a density above the sensitivity threshold of the photocopy machine.</p> |
