1. A method for detecting printing defects, the method comprising: with a physical computing system, creating a matched reference image from a digital image, colors of said matched reference image being closer matched to a scanned image of said digital image; with said physical computing system, determining a color difference between corresponding points on said matched reference image and said scanned image; and with said physical computing system, identifying points that have said color difference greater than a predefined threshold as potential defects, wherein forming said matched reference image comprises: with said physical computing system, for a range of color values for a color channel, determining an average color difference between corresponding pixels within said digital image and said scanned image for said range; and with said physical computing system, adding said average color difference to color values of said digital image within said range to form said matched reference image.