Currency verification

Apparatus for verifying authenticity of a certificate under test, wherein an authentic version of the certificate has a known watermark in a predetermined watermark region thereof, the apparatus comprising:

• an image sensor, which is adapted to capture an image of at least a portion of the watermark region of the certificate under test and to generate an output signal responsive thereto;
• and
• an image processor, coupled to receive the output signal, and adapted to process the signal so as to find a correlation between the image of the watermark region and the known watermark and, responsive to the correlation, to register a portion of the image of the watermark region with the known watermark, the image processor being further adapted to measure a range of intensity values in the registered portion of the image, to define a vector in a decision space, the vector having coordinates given by the range of the intensity values and by a value of the correlation between the image of the watermark region and the known watermark, and to determine the certificate under test to be authentic if the vector falls within a predefined area of the decision space.