Patent US 4,139,779

A method is provided for automatically assessing a printed article, in particular a bank-note. The sample to be assessed is compared point by point with an original and differential values are thereby formed between the reflectance values obtained by photoelectrical scanning from the individual image points of the sample and the reflectance values of the image points of the original corresponding to the sample image points. The differential values of each image point are added, in the correct sign, with predetermined weighting, to the differential values of the image points adjacent thereto, and the sample is assessed as faulty if the absolute amount of the added differential values exceeds a predetermined threshold value at least in one image point.