Detection of counterfeit objects, for instance counterfeit banknotes

DETAILED DESCRIPTION It is an object of this invention to provide an improved method and apparatus of detecting counterfeit objects.
According to one aspect of the present invention there is provided apparatus for detecting counterfeit objects comprising means for illuminating the object with light within a first wavelength band, a detector for detecting light from said object having a first wavelength within said first wavelength band and a second wavelength within a second wavelength band different from said first wavelength band and said second wavelength band including wavelengths at which counterfeit objects may fluoresce when exposed to light in said first wavelength band, comparison means for comparing the output of the detector with at least one reference level and decision means for deciding, based on said comparison whether said object is counterfeit or not and providing an appropriate indication.
According to another aspect of the present invention there is provided apparatus for detecting counterfeit objects comprising a detector for providing a first signal indicative of the reflectivity of an object within a first wavelength band and a second indicative of the fluorescence of the object within a second wavelength band different from said first wavelength band and decision means for deciding, based on said first and second signals, whether said object is a genuine banknote and for providing an appropriate indication.
Various further aspects of the invention are set out in the accompanying claims.
It has been discovered that genuine and counterfeit banknotes often have different reflectivities particularly when exposed to ultraviolet radiation in the band of from 300 to 400 nm.
It has also been discovered, somewhat surprisingly, that when the reflectivities of genuine and counterfeit notes are similar, the fluorescence exhibited by the notes is usually dissimilar, and vice versa.
Thus by applying two tests to sense both the fluorescent light and the reflected light from a banknote exposed to ultraviolet radiation, a banknote can be declared genuine or counterfeit with great certainty