| 摘要 |
A document for which a high degree of security is needed, e.g. a debit card, has on it patches of an obliquely-reflective foil material such as aluminium foil with closely spaced angled spinules. This looks dark from one angle and rather silvery from another angle. The value-indicating patches for a credit card each consists of a spot of such material. Various methods of cancellation of the dots are described. <IMAGE> |
