“…Many approaches are also based on textures [2,10,16,17,18,21,22] and/or on edges [7,14,16,21]. In a few works more complex features are also used, for example based on entropy of the pixel values [21], or shape [10]. Features are extracted either from the whole image [21], or from regions obtained by a predefined rectangular block subdivision [2,14,17,18,20] or by image segmentation [7,10].…”