Patent ID: 7684607

Claim:
A method for automatic discrimination of the authenticity of a document being one of currency notes, security instruments, security documents and similar documents complementing manual discrimination, said method comprising: a) irradiating an inspection area of the document with a light source that emits radiation having wavelengths corresponding to UV visible electromagnetic waves and optionally near infrared electromagnetic waves; b) acquiring reflected/fluoresced light from said inspection area of the document to generate a plurality of reflected/fluoresced signals; said document under inspection being held in a stationary condition; said reflected/fluoresced light having wavelengths corresponding to UV visible electromagnetic waves and optionally near infrared signals comprising at least 3 reflected/fluoresced signals S 1 , S 2 and S 3 , each of said three reflected/fluoresced signals being generated by a corresponding detector coupled to a band pass filter having different pass wave bands (λ 1 , λ 2 and λ 3 ) being given by: S 1 =∫∫∫k 1 (λ).{ r λ 1 ,x,y (λ, x,y )/( x 2 +y 2 +z 2 )} dλdxdy S 2 =∫∫∫k 2 (λ).{ r λ 2 ,x,y (λ, x,y )/( x 2 +y 2 +z 2 )} dλdxdy S 3 =∫∫∫k 3 (λ).{ r λ 3 ,x,y (λ, x,y )/( x 2 +y 2 +z 2 )} dλdxdy where spatial integration is taken over the surface area of the document of interest and wavelength domain integration is taken over the wave band of interest, where_k(λ): a wavelength dependent constant of proportionality indicating energy conversion efficiency of the photodetector and filter combination, where r λ1, x,y, r λ2, x,y and r λ3, x,y : average value of reflectance corresponding to the three optical filters at corresponding wavelengths at x, y, where b(λ,x,y): incident energy depends upon the source type and its location; and where x,y: coordinates of the centre point of an elementary area taking the foot of the normal drawn from the detector surface to the plane of the document under authentication as the origin z represents a vertical distance; c) defining a set of dimensionless ratios using the at least 3 reflected/fluoresced signals S 1 , S 2 and S 3 and calculating using a processor a measured dimensionless ratio value in respect of each of the said dimensionless ratios thus defined; and d) comparing, using the processor, each of the measured dimensionless ratio values with a predefined dimensionless ratio value to judge the authenticity of said documents.