1. A method for automatically classifying a printed image, comprising: scanning the printed image; selecting an n by n block of pixels from the scanned image; calculating an array of DCT coefficients of the pixel block, wherein the calculated DCT coefficients are representative of spatial frequency and spatial orientation of the pixel block; inputting the array of DCT coefficients into a classifier which has been configured to identify different image marking processes used to produce printed images using DCT coefficients; and determining an image marking process used to create the printed image based on the array of DCT coefficients.