Weapon identification is based on the agreement found by comparative analysis of the individual characteristics of marks left by the weapon on respectively the evidence and the test ammunition components. The latter instrument is a special microscope which allows the comparison of two projectiles by presenting to the expert's eye overlapping images of both projectiles. The expert is able to manipulate the projectiles until maximum correspondence between the images is reached. The main approach consists of studying different types of image registration techniques, based on correlation. Preliminary results show already that the reliability of classical correlation is limited, due to its sensitivity to noise and to differences in scale and rotation.
Alternative techniques are currently under study.