How Does Fingerprinting Work

Fingerprinting method is also known as dactyloscopy. It is a method wherein, fingerprints of a person are knowingly or unknowingly picked up and recorded in a special computerized system. This system helps to maintain the fingerprint impressions for future use and is extremely useful for comparing and verifying if two sets of fingerprints belong to the same person or not. This system may either be used for creating a database of employees for organizational records or for records with the law and order departments, in case a person is held under suspicion. Let us now see how the fingerprinting technique works.

Uniqueness of Fingerprints

As part of the evolutionary process, we human beings have developed a unique combination of friction ridges or the tiny network of crisscrossing lines all over our palms and soles. But have you ever wondered when we develop these ridges in the first place? Well, these ridges and lines on the palms appear when we are in our mother's womb. On account of roughness of these ridges, we can get a better grip on things that we try to hold, just like the effect of rough tire surface on a slippery road. Nature works wonders all the time and it is interesting to know that no two persons in this world have same fingerprints. A recording of fingerprints has a higher chance of perfectly identifying criminals than even competing test like DNA analysis. After all, siblings in a family or twins are likely to have a similar DNA structure.

Categories Of Fingerprints

1. Exemplar Prints: This method refers to deliberate collection of fingerprint samples by scanning the palms of suspects in a crime, or by applying a layer of dark printing ink on a suspect's palm and taking its impression on a fingerprint sample card. This method is also used in organizations as part of joining formalities for a new employee. At times, this method is used by banks for making signature cards for customers who may be illiterate, or not in a position to sign.
2. Photographic Images: At times, records of fingerprints are maintained by taking close-up pictures of the palms of a person. These pictures may later be compared to other samples of a person's fingerprints.
3. Latent Prints: Just as the word means, latent images are absolutely invisible to a naked eye. However, they might be revealed on closer scrutiny of an object, or under the focus of a light. These prints are made unintentionally by a person as he touches solid objects with his palms and fingers. In a crime scene, latent prints are known to overlap with different prints and get distorted. There is often a mixture of contamination in the form of human perspiration, ink, blood, grease or just plain oil and dirt. Due to their distorted nature, latent prints are less reliable and tedious to work with.
4. Patent Prints: Unlike latent prints, patent prints are very much visible to the human eye. They are made on flat surfaces or on the floor on account of wet mud or clay, blood, ink or plain powder. Such prints are much easier to verify and maintain than latent prints. Patent prints can be recorded using photography too.
5. Plastic Prints: This is a rare sample of fingerprints where impressions are unintentionally made in wet soil or in a soft clay ball or dough. Generally, the materials are thick enough to retain the impressions of fingerprints and make verification process quite easy as they are noticeable.

Collection and Verification of Fingerprints

• The frictional ridges or epidermal ridges are likely to create an imprint of their design structure on account of their vibration as they casually brush any smooth surface. These impressions might be created on account of contamination of palms with dirt or just plain excretion of minuscule quantity of perspiration from the surface of these ridges.

• Categories like exemplary prints, plastic prints, patent prints provide direct impressions of fingerprints which can either be stored or photographed as proof. However, latent prints are difficult to capture. Traditionally, these impressions were highlighted for photographs by gently spreading a special powder over it. These prints were then tested by any of the following three popular methods:

• Henry Classification System
• The Roscher System
• Juan Vucetich System

• The Henry classification system in particular, has been popularly used in most English-speaking countries. This system gives importance to three basic patterns in fingerprints viz. loops, arches and whorls. The right hand is coded as 'R' while the left hand is coded as 'L'. Similarly, the five different fingers are identified as 't' for thumb, 'I' for index finger, 'm' for middle finger, 'r' for ring finger and 'p' for the little finger. There are different numerals attached to fingers depending upon the presence of loops or whorls. A fraction is created to arrive at a particular digit, the formula for which is as follows:

Ri/Rt + Rr/Rm + Lt/Rp + Lm/Li + Lp/Lr = (Ri + Rr + Lt + Lm + Lp)/(Rt + Rm + Rp + Li + Lr)

The answer to the fraction helps to identify the sets with which the fingerprints are to be matched. For e.g., a fingerprint with fraction answer as 5 will need to be compared only with previous fingerprint samples with answer 5 and so on.

• Modern methods involve usage of chemicals from fingerprint analysis labs. Chemicals such as diazafluorenone and ninhydrin are popularly used for this purpose. Some techniques include vacuum metal deposition and ethyl cyanoacrylate polymerisation. One may also use an instrument called Kelvin probe on the crime scene. With modern technology, fingerprint analysis has become perfect like never before.

Some Interesting Facts

• Fingerprints, especially latent prints, help to verify if the person is a drug abuser or not. This is done by analyzing the contents of sweat in the latent prints.
• Fingerprints of young children, who are yet to reach puberty, have lower levels of oil or wax content. Hence these prints have a high chance of disappearing faster.
• Fingerprints cannot be altered by any person through intentional or unintentional scars. The structure of frictional ridges re-emerge as the wound heals.
• In rare cases, when a criminal tries to alter the imprints of his fingertips, by skin grafting, it is still possible to analyze his fingerprints by ridges on the rest of the palm.

Dactyloscopy happens to be a significant part of forensic science study too. This is such an interesting science that it has now gained usage in fields other than crime investigation. With a rise in its importance, we can expect many more scientific innovations in this technique. On account of its importance, this field can also be treated as a good career option for the youth.