18. The device according to claim 17 , wherein said digital signal processing unit is implemented as an FPGA (Field-Programmable-Gate-Array) unit.
17. A device for checking the authenticity of security documents, in particular banknotes, according to the method of claim 1 , comprising an optical system for acquiring the sample image of the region of interest and a digital signal processing unit programmed for performing the digital processing of the sample image.