METHOD FOR PREVENTING THE SUCESSFUL FORGERY OF DOCUMENTS AND DEVICE THEREFOR

摘要

A security blank is formed with a light-redirecting spatial structure including a deterministic component establishing at least one authenticating feature, and a stochastic component superimposed on the deterministic component, and sufficiently obscuring the deterministic component so as largely to frustrate recognition of the function of the authenticating feature by intensity measurement of light reflected therefrom. Recognition of the function of the authenticating feature is made possible by a method and an apparatus measuring the degree of coherence of two narrow bundles of light rays obtained from light reflected from the spatial structure upon its illumination by light of a selected wavelength.