SECURITY DOCUMENT VALIDATION

摘要

This invention concerns a method and apparatus for validating banknotes. In a number of countries, genuine banknotes are provided with a security thread which is embedded within the banknote but partially exposed at regularly spaced regions along its length by windows. These windows are of greater width than the security strip itself, and in this invention the increased transmissivity of the banknote, in particular in the infrared region, is utilised to detect the presence of such windows in order to validate the banknote. If the required variation in transmissivity is not detected, the banknote can be rejected as a counterfeit.