a system for and method of assessing fluid spray using image processing techniques of a calibration and one or more as - sprayed witness cards . calibration and as - sprayed witness cards are exposed to a backlight sufficient to make a plurality of stains thereon electronically visible . at the same time an image of the stains is captured by , e . g ., a digital camera . resulting image data is processed to assess characteristics of the stains of the fluid on the as - sprayed witness card and thereby assess characteristics of the spray , e . g ., volume of fluid delivered . in one embodiment , the witness card is a chemically coated semiopaque plate .