The identification of an individual by his fingerprints is the oldest of the biometric techniques. A logical fact if we think that the vast majority of the population has unique and unalterable fingerprints. But what are fingerprints? How are they formed? Are they really unique and differentiate us from others? And finally, can we impersonate our identity with a fake fingerprint? To these and other questions we will give answers in the blog of Umanick with a series of articles, where we will analyze the fingerprint in depth.
The accuracy of identification of people by fingerprints, and the fact that users have enough knowledge on how to use it, makes it the most widespread biometric method, with a large number of applications in everyday life.
Fingerprints. Image of Alan Levine with a Creative Commons license.
As a starting point, it can be said that it is based on the analysis of the impression produced by the rough part of a person’s finger on a smooth surface. This roughness of the finger presents a series of ridges -called papillary crests- that make up a very characteristic pattern. This is defined during the fetal development of the person and is unique to each individual. No two are the same, even in identical twins.
The papillary crests are sweat secretion glands located in the dermis (sweat glands). When the sweat goes out, it spills over the crests and mixes with the natural fat of the skin, causing that when an object apt for the retention of traces is manipulated, they remain imprinted in the same one.
How and why fingerprints are formed
The fingerprints are not there only so that the TV actors Grissom and Horatio of CSI can identify the criminals. The main function of the ridges and grooves of the fingertip of our fingers is to detect fine textures and tiny objects to the touch.
The fingerprints develop between the second and sixth months of pregnancy, appearing on the inner surface of the dermis as ripples that will develop later as lines that will contain the ducts of the sweat glands. At 18 weeks, the fetus has already fully formed fingerprints.
The middle layer of the skin of the fingertips begins to grow faster than the inner and outer layers, and this causes the papillary crests to originate. The exact design of the papillary ridges is determined by the composition of the amniotic fluid and by the way the fetus touches what is around it while moving.
For a long time it was thought that fingerprints facilitated the process of grabbing objects, but a study carried out in 2009 at the University of Manchester found that making it harder to hold flat surfaces. They may be useful when holding rough objects, but if this were their main function, we would have fingerprints all over the hand. What is clear is that they improve our tactile sensitivity by amplifying small vibrations each time our fingers touch a surface.
Properties of the fingerprint
It is scientifically proven that the papillary drawings, that is to say, the drawings that form the impression of the fingerprint, are permanent, immutable and diversiform. They are permanent because, since their formation, they remain unchanged in number, situation, form and direction.
They are immutable because the papillary ridges can’t be physiologically modified. In fact, if there is a shallow trauma, they regenerate and, if it becomes deep, the ridges do not reappear in a different form than they had, but the part affected by the trauma is invaded by a scarred pattern.
They are diversiform, since it has still not been the case to find two identical impressions produced by different fingers. These three properties make the fingerprint a very secure identification method and, consequently, one of the most recognized among all existing biometric techniques.
The fingerprint is used in many applications in which the identification of people is wanted in a safe and comfortable way for the user. Its objective is to avoid the risks of identity theft derived from the theft, copy or loss of cards and numerical codes, in a very practical way for the user, avoiding having to remember codes or passwords.