The police will take fingerprints when dealing with criminal cases. Fingerprints, also known as handprints, are ridges protruding from the epidermis. Because people's fingerprints are generated by the interaction of heredity and environment, everyone has fingerprints, but they are different. Because the fingerprint repetition rate is very small, about 654.38+0.5 billion, it is called "human ID card". Fingerprint is a line formed by the concave and convex skin of human fingertips. Fingerprint can increase the friction when the hand touches the object, so it is easier to exert force and grasp the object. It is naturally formed in the process of human evolution. Fingerprint extraction from crime scene is an extremely important link.