Patent ID: 7403272

Claim:
A method for the identification of banknotes and documents marked with OVI™ inks (Optical Variable Inks), providing the following phases: generating a light ray; polarizing that light ray through a first polarizing filter ( 3 ), and sending a polarized ray ( 4 ) onto a marked area ( 5 ) to be assessed; filtering the ray ( 6 ) reflected by the area ( 5 ) which is to be assessed by means of a second polarizing filter ( 7 ), in anti-phase with the first polarizing filter ( 3 ) and measuring the luminous intensity of such a reflected ray ( 6 ) already filtered, so getting a first signal s a ; filtering the ray ( 6 ) reflected the area ( 5 ) to be assessed by means of a third polarizing filter ( 8 ), in phase consistency with the first polarizing filter ( 3 ), and measuring the luminous intensity of such a reflected ray ( 6 ) already filtered, so getting a second signal s b ; measuring the difference Δ between these two signals s b and s a ; compare the calculated value Δ to a reference value Δ r previously measured on genuine documents and banknotes.