fingerprint, an impression of the underside of the end of a finger or thumb, used for identification because the arrangement of ridges in any fingerprint is thought to be unique and permanent with each person (no two persons having the same prints have ever been found). Palm prints and footprints are also used, especially for identification of infants. Traditionally, impressions have been taken from a person using ink and paper, but in live-scan fingerprinting electronic images produced by a video scanner are converted by computer into binary codes, which can be more readily compared.
As an identification device, fingerprinting dates from antiquity, but modern systems began essentially with the work of Henry Faulds, William James Herschel, and Sir Francis Galton in the late 19th cent. Fingerprints gained acceptance as a more objective form of identification than visual recognition. The Galton method, elaborated by E. R. Henry, is still used in Great Britain and the United States. Juan Vucetich in Argentina, also using Galton as a guide, developed (1904) an alternate system that gained wide acceptance in Spanish-speaking countries.
Fingerprinting for identification of criminals was first used in connection with the Bertillon system. Most countries now require that all criminals be fingerprinted. Methods have also been devised for developing fingerprint impressions left by criminals at the scene of a crime. The most common uses a brush and powder to mark the fingerprint, which is then photographed and lifted from the surface using tape. The reliability of fingerprints for criminal identification is complicated by the need to use crime scene prints that may be partial or distorted and by the technical competency of the person identifying the print (computer identification is often used as an aid).
In 2002 a federal judge ruled that, because of inconsistencies in laboratory identification of fingerprints, fingerprint identification as practiced was not accurate enough to be used without qualification, and that an expert cannot testify that a person's fingerprints absolutely match those found at a crime, though an expert may point out similarity between two sets of prints and may state that no two people have identical prints. The judge reversed himself two months later, deciding that although the FBI's fingerprint identification procedures were not proven scientifically according to a strict standard they were nonetheless sufficiently reliable.
In the United States, prints also are taken of civilian government employees and members of the armed forces and by some banks and other agencies. Some states now require a thumbprint when applying for a driver's license, and banks and check-cashing institutions are increasingly requiring a thumbprint before cashing checks, particularly in states that use license thumbprints. Some stores also require thumbprints when paying by check or even by credit card. A national fingerprint file and database is maintained by the Federal Bureau of Investigation.
See C. Beavan, Fingerprints (2001), and S. A. Cole, Suspect Identities (2001). Technical works on the subject include H. C. Lee and R. E. Gaensslen, ed., Advances in Fingerprint Technology (2d ed., 2001), D. R. Ashbaugh, Quantitative-Qualitative Friction Ridge Analysis (1999), and D. L. Faigman et al., Modern Scientific Evidence (2d ed., 2002).