1 : A digital image acquisition device, comprising (a) an image acquisition sensor, (b) a shutter, (c) optical elements for focusing an image on the sensor, (d) an aperture disposed between said optical elements and said shutter, (e) a translucent lens cap which defocuses images when in place, and (f) digitally-embedded programming such that the device is arranged to automatically capture a calibration image of a de-focused scene when said shutter and said aperture are open, and to derive a map of defects from the calibration image acquired by the sensor when illuminated by ambient light.