Footwear impressions and tire impressions are examined in the same fashion. Impressions can be three-dimensional when left in snow or soft soil, or they can be two-dimensional when a dirty, bloody, or other impression is left on a hard surface. Footwear impressions can be as individual as a fingerprint. There may be thousands of other people that have the exact same shoe as you, yet your shoe impression may be unique. As you wear your shoe, the tread wears down uniquely to your walking style. Also, accidental scratches, nicks, and cuts are left on the bottom of your shoe, which may be unique. Tires undergo the exact same changes making them unique as well.
Questioned impressions from crime scenes can be photographed, lifted, or cast with dental stone to compare to suspect shoes or tires. A comparison of tread designs or wear patterns can lead to a positive identification.