Importance

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Abstract

In an apparatus and a method for examining the authenticity of a document, which includes at least a machine-readable authenticity feature in the form of an optical microstructure for diffracting at least one component of a beam of light rays which has a wavelength of a first predetermined value and impinges on the microstructures along a predetermined direction, a light source for emitting the beam of light rays, and wherein the components of the light rays diffracted from the microstructure have an intensity distribution defining an effective center line of 'gravity' along one direction of diffraction, a light-sensing device for sensing the light rays diffracted from the microstructure and for generating electrical signals from the sensed light rays, and an evaluator for processing the electrical signals generated by the light sensor, and for deriving from information contained in the processed electrical signals a YES/NO decision whether the document is authentic or not, there is provided a control connected to the light source so that the light source switches the wavelength of the beam of light rays from the first predetermined value to a second predetermined value, and wherein the evaluator provides the YES decision if the shift between the center lines of gravity of the intensity distribution of the components of the light rays diffracted by the microstructure lies between predetermined limits.

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First Claim