To improve the image quality of criminal photography through surface treatment on the metallic trace carrier to upgrade the imaging quality in ordinary environment of visible light sources. The imaging characteristics of traces with shapes of line and concave formed on the surface of Al and Pb boards were investigated by an optical microscope with different light sources. The dispersion phenomena under high magnification were analyzed in order to validate their effects on the imaging quality. After pre-processing of traces on the metal surface with mixed solution of absolute ethyl alcohol and 50% (mass fraction) acetone, the imaging quality was tested and the causes of changes were discussed. Tiny lines in the traces on the metal surface could lead to optical interference, which resulted in the formation of light and dark stripes with different colors in the optical microscope photomicrograph. Proper treatment of traces on metallic trace carrier with special etching solution can eliminate interference of trace carrier in the optical imaging system. Pretreatment of traces on metal surface with this method can improve the imaging quality of tiny trances in photomicrography.