Fingerprints – From Womb to Biometric Scanner

Types of fingerprint

For forensic purposes, there are two types of fingerprints that can be left behind: visible and latent. Latent fingerprints are made from the sweat and oil on the skins surface and are invisible to the naked eye whilst visible fingerprints are easily visible to the naked eye and made up from substances such as blood, grease, ink, or dirt or even three dimensional impressions made by pressing your finger in things such as fresh paint, wax, soap, or tar.

For biometric devices, the type of fingerprint left behind holds less importance as they are not being collected in the same way as required by a forensic investigation and are not interested in the what and why that may arise from the types of fingerprint briefly described above. Instead it is all about how the fingerprint is read and analysed by technology.

How are fingerprints read

Initially the general patterns type of a fingerprint is used to make initial comparisons and narrow the print down to a group but not an individual. The three general pattern types are loops, whorls and arches which could also be subcategorized as shown in the image. Loops are the most common pattern type appearing in 60 – 65% of fingerprints, consisting of ridges that enter on one side, loop around and exit on the same side. Arches are the least common type of fingerprint pattern, only occurring roughly 5% of the time and is characterised by ridges that enter on one side of the finger and exit on the other with a sight arch somewhere in between.  Finally, whorls are seen around 30 – 35% of the time and represent a circular flow.

After this initial comparison, specific and distinctive points of the fingerprints are compared, known as minutiae. These small irregularities are what make fingerprints unique to each individual and can be defined as the points where the ridge lines end or fork. There are three major types of minutiae features: the ridge ending, the bifurcation, and the dot (also called short ridge). The ridge ending is, as indicated by the name, the spot where a ridge ends. A bifurcation is the spot where a ridge splits into two ridges. Spots are those fingerprint ridges that are significantly shorter than other ridges.

Different types of scanners, work in different ways but all with the same goals in mind. The scanner system does not have to match every minutiae that could be found in both the sample and fingerprint on record, but find enough of a matching sample in order to determine that the prints match. The exact number of matches needed varies according to the scanner but the more minutiae that are matched the higher the probability that the fingerprint is a match.