| 摘要 |
A substrate, such as a document of value, carries a design feature (F) which comprises an array of repeating patterns, the patterns exhibiting discrete differences in one or more visual characteristics (e.g. shape or colour or optical responses) according to a predetermined pattern. The differences are preferably indiscernible to the unaided eye but can be discriminated by an optical reading machine. In alternative embodiments, the visual characteristics of each pattern represent 8- or 16-bit information. |
