A document processing system and a method for classifying an input image or region thereof as either a synthetic graphic or a natural picture, is disclosed. The system includes an image input subsystem, a processing subsystem for processing image data provided by the image input subsystem, and software/firmware means operative on the processing subsystem for a) low-pass filtering image data representative of the input image or region thereof to produce low-pass filtered pixel values; b) determining a smoothness value for each of a plurality of low-pass filtered pixel values; c) generating histogram data from the smoothness values; d) determining a texture metric for the input image or region thereof from a subset of the histogram data; and e) thresholding the texture metric to classify the input image as either a synthetic graphic or a natural picture.