A high resolution image of a CCD camera subassembly is examined to determine whether dust is present inside the subassembly. By examining the size, number, and location of the dust particles it can be determined whether the dust is likely to cause issues when the camera subassembly is integrated into a fully assembled document scanner. Other contaminants and defects, such as scratches on the glass covering, can also be detected. This method can be used as the acceptance criteria of individual camera subassemblies from the manufacturer.