Biometric modality: Fingerprint – what is it?
Fingerprints are formed by the raised papillary ridges that run across the skin’s surface. Humans, together with some other mammals, have these ridges on their fingers, thumbs, palms and the toes and soles of the feet. The ridges have evolved to provide friction in order to aid grip and locomotion. The flow of these ridges often forms patterns but the ridges themselves do not always run continuously due to breaks and deviations in their structure (i.e. where the ridges end or bifurcate – known as minutiae). The occurrence of these minutiae is random in nature and are used as the basis for establishing identity as no two regions of skin, bearing papillary ridge systems, have ever been found to have the same arrangement of minutiae. Consequently, the fingerprints on each human digit are unique and can be used to identify individuals. The same is true of palmprints but the area of ridged skin is much larger and therefore contains more detail. Some biometric systems use palm prints or palm prints together with fingerprints to enrol individuals.
Biometric recognition systems capture and digitise salient features from the fingerprint such as the arrangement of minutiae and the flow and orientation of the ridges to create a biometric template. These templates are then stored in a dataset that allows the system to select fingerprints to perform either individual comparisons or searches through the appropriate database(s) depending on the use case.
Fingerprints can be recorded using paper and ink but most current biometric applications use either a scanner, where the finger is placed on or rolled across a platen, or a contactless method that captures the required detail at a proximal distance. This method is becoming increasingly popular because of the potential hygiene issues associated with multiple enrolments on the same platen. However, any of these enrolment methods require cooperation from the subject and often human supervision at the time of enrolment to assure the quality of the biometric data.