When an item of footwear comes into contact with a surface a two or three dimensional mark or impression may be left on that surface.
2-D prints are left when a shoe stands on a hard, flat surface and can be left in ink, blood or dust for example. The mark would be photographed by a Scene Examiner, possibly enhancing it with fingerprint powder. The mark can then be lifted from the surface using an adhesive lifter such as a gel lifter. Sometimes the mark is not removed at all, but the item bearing the mark is submitted directly to the forensic scientist for examination e.g. an envelope, table or door.
3D prints are found on soft surfaces such as mud or snow and when the shoe has sunk into the medium. A plaster cast can be made of the impression so that it can be retained for further examination.
Footwear marks and impressions can contain details of the pattern, size and degree of wear from the item, each of which provides additional clues for the forensic scientist in their analysis.
Specific damage features are made on the sole/heel areas of footwear during use and these can be reproduced in marks and impressions that have been left at the crime scene. This damage detail is acquired in a random manner and may be regarded as a characteristic of a particular item of footwear. Such damage will be unique to that particular item of footwear.
Comparison of an item of footwear with a mark or impression generally involves the making of test marks in the laboratory and this enables the forensic scientist to determine whether any relationship exists between the footwear recovered from the suspect and the mark or impression found at the crime scene.