In an apparatus for processing banknotes or other sheet-like objects, the banknotes are conveyed along a transport path, thereby passing sensor means. A transmission and a reflection image of the banknote are captured by illuminating the banknotes and measuring the transmittive and reflective light intensity of light with a high resolution. Based on these images, a validation of the banknotes is carried out. After the validation, a double feed detection is performed by evaluating the transmission and the reflection intensities for a predefined set of test spots with a two-dimensional evaluation. If it is decided on double feed, the banknotes are rejected. Otherwise the banknotes are accepted and further processed. Because of the additional dimension in the evaluation compared with known double detection methods, the invention enables a more robust double note detection also in cases with different degrees of soiling of the banknotes.
