A image processing unit, and particularly to a one-button-triggered image processing unit capable of processing image data automatically. This one-button-triggered image processing unit comprises a button for inputting a trigger signal so as to start on the operation of the unit; a prescan module for prescanning a target at a first resolution; a target image calculation module for calculating the first image area; a target image marking module for marking out the target image contour in the first image; a scan module for scanning the target at the second resolution assigned by a user; a target image processing module for filtering impurities and straightening on the target image of the second image area; and a crop module for abstracting the target image by the marked contour in the second image and trimming the edge of the abstracted target image to get a target the same size as the scanned target.