Abstract: Light source is critical for photograph quality. Experiments with different illumination methods and light sources were conducted. Firstly, a photo of normal cube with CCD camera was taken. Secondly, iterative average filter method was used to deal with image collected to reduce interference caused by noise in detecting edge. Thirdly, 1D gray moment sub-pixel method was used to detect edge of normal cube. Finally, average algorithm was used to calculate thickness of every normal cube to test the impact of illumination system on image detection accuracy. The test shows that illumination error of apheliotropic light for medical observation is the minimum.