An apparatus and method are provided for processing a digital image to determine whether the image includes a region of differential gloss (which would yield a differential gloss when that digital image is printed into hardcopy). The method includes identifying whether an input digital image has a periodic characteristic which is indicative of a cluster screen halftoned digital image and, if so, determining a correlation between first and second filters and halftone structures of the identified digital image. The second filter has a different polarization from the first filter. The first and second filters are selected to enable a region of differential gloss in the identified digital image to be identified, based on the determined correlations. Where such a region or regions are detected, a representation of the differential gloss image may be displayed and/or another action automatically initiated, such as restricting printing of the image.