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Biometrics | Biometrics in popular culture |performance of biometric systems |

Biometrics comprises methods for uniquely recognizing humans based upon one or more intrinsic physical or behavioral traits. In information technology, in particular, biometrics is used as a form of identity access management and access control. It is also used to identify individuals in groups that are under surveillance.

Biometric characteristics can be divided in two main classes:
  • Physiological are related to the shape of the body. Examples include, but are not limited to fingerprint, face recognition, DNA, hand and palm geometry, iris recognition, which has largely replaced retina, and odor/scent.
  • Behavioral are related to the behavior of a person. Examples include, but are not limited to typing rhythm, gait, and voice. Some researchers have coined the term behaviometrics for this class of biometrics.
Strictly speaking, voice is also a physiological trait because every person has a different vocal tract, but voice recognition is mainly based on the study of the way a person speaks, commonly classified as behavioral.


It is possible to understand if a human characteristic can be used for biometrics in terms of the following parameters:
  • Universality – each person should have the characteristic.
  • Uniqueness – is how well the biometric separates individuals from another.
  • Permanence – measures how well a biometric resists aging and other variance over time.
  • Collectability – ease of acquisition for measurement.
  • Performance – accuracy, speed, and robustness of technology used
  • Acceptability – degree of approval of a technology.
  • Circumvention – ease of use of a substitute.
A biometric system can operate in the following two modes:
  • Verification – A one to one comparison of a captured biometric with a stored template to verify that the individual is who he claims to be. Can be done in conjunction with a smart card, username or ID number.
  • Identification – A one to many comparison of the captured biometric against a biometric database in attempt to identify an unknown individual. The identification only succeeds in identifying the individual if the comparison of the biometric sample to a template in the database falls within a previously set threshold.
The first time an individual uses a biometric system is called an enrollment. During the enrollment, biometric information from an individual is stored. In subsequent uses, biometric information is detected and compared with the information stored at the time of enrollment. Note that it is crucial that storage and retrieval of such systems themselves be secure if the biometric system is to be robust. The first block (sensor) is the interface between the real world and the system; it has to acquire all the necessary data. Most of the times it is an image acquisition system, but it can change according to the characteristics desired. The second block performs all the necessary pre-processing: it has to remove artifacts from the sensor, to enhance the input (e.g. removing background noise), to use some kind of normalization, etc. In the third block features needed are extracted. This step is an important step as the correct features need to be extracted in the optimal way. A vector of numbers or an image with particular properties is used to create a template. A template is a synthesis of the relevant characteristics extracted from the source. Elements of the biometric measurement that are not used in the comparison algorithm are discarded in the template to reduce the filesize and to protect the identity of the enrollee.

If enrollment is being performed the template is simply stored somewhere (on a card or within a database or both). If a matching phase is being performed, the obtained template is passed to a matcher that compares it with other existing templates, estimating the distance between them using any algorithm (e.g. Hamming distance). The matching program will analyze the template with the input. This will then be output for any specified use or purpose (e.g. entrance in a restricted area).

Fingerprint types

Latent prints

Although the word latent means hidden or invisible, in modern usage for forensic science the term latent prints means any chance of accidental impression left by friction ridge skin on a surface, regardless of whether it is visible or invisible at the time of deposition. Electronic, chemical and physical processing techniques permit visualization of invisible latent print residue whether they are from natural secretions of the eccrine glands present on friction ridge skin (which produce palmar sweat, consisting primarily of water with various salts and organic compounds in solution), or whether the impression is in a contaminant such as motor oil, blood, paint, ink, etc. There are different types of fingerprint patterns such as an arch, tented arch, a loop, and a whorl. Each indicate what type of fingerprint it is.
Latent prints may exhibit only a small portion of the surface of the finger and may be smudged, distorted, overlapping, or any combination, depending on how they were deposited. For these reasons, latent prints are an “inevitable source of error in making comparisons,” as they generally “contain less clarity, less content, and less undistorted information than a fingerprint taken under controlled conditions, and much, much less detail compared to the actual patterns of ridges and grooves of a finger.”

Patent prints

These are friction ridge impressions of unknown origins which are obvious to the human eye and are caused by a transfer of foreign material on the finger, onto a surface. Because they are already visible they need no enhancement, and are generally photographed instead of being lifted in the same manner as latent prints. An attempt to preserve the actual print is always made with numerous techniques; for later presentation in court. Finger deposits can include materials such as ink, dirt, or blood onto a surface.

Plastic prints

A plastic print is a friction ridge impression from a finger or palm (or toe/foot) deposited in a material that retains the shape of the ridge detail.[7] Commonly encountered examples are melted candle wax, putty removed from the perimeter of window panes and thick grease deposits on car parts. Such prints are already visible and need no enhancement, but investigators must not overlook the potential that invisible latent prints deposited by accomplices may also be on such surfaces. After photographically recording such prints, attempts should be made to develop other non-plastic impressions deposited at natural finger/palm secretions (eccrine gland secretions) or contaminates

The following are used as performance metrics for biometric systems:

  • false accept rate or false match rate (FAR or FMR) – the probability that the system incorrectly matches the input pattern to a non-matching template in the database. It measures the percent of invalid inputs which are incorrectly accepted.
  • false reject rate or false non-match rate (FRR or FNMR) – the probability that the system fails to detects a match between the input pattern and a matching template in the database. It measures the percent of valid inputs which are incorrectly rejected.
  • receiver operating characteristic or relative operating characteristic (ROC) – The ROC plot is a visual charactization of the trade-off between the FAR and the FRR. In general, the matching algorithm performs a decision based on a threshold which determines how close to a template the input needs to be for it to be considered a match. If the threshold is reduced, there will be less false non-matches but more false accepts. Correspondingly, a higher threshold will reduce the FAR but increase the FRR. A common variation is the Detection error trade-off (DET), which is obtained using normal deviate scales on both axes. This more linear graph illuminates the differences for higher performances (rarer errors).
  • equal error rate or crossover error rate (EER or CER) – the rate at which both accept and reject errors are equal. The value of the EER can be easily obtained from the ROC curve. The EER is a quick way to compare the accuarcy of devices with different ROC curves. In general, the device with the lowest EER is most accurate. Obtained from the ROC plot by taking the point where FAR and FRR have the same value. The lower the EER, the more accurate the system is considered to be.
  • failure to enroll rate (FTE or FER) – the rate at which attempts to create a template from an input is unsuccessful. This is most commonly caused by low quality inputs.
  • failure to capture rate (FTC) – Within automatic systems, the probability that the system fails to detect a biometric input when presented correctly.
  • template capacity – the maximum number of sets of data which can be stored in the system..
As the sensitivity of the biometric device increaes, the FAR decreases but the FRR increases.

Biometrics in popular culture
  • Biometric technologies have been found in a number of popular cinema released films. This alone has created an interest, from general consumers, as a means of identifying ones self. In 2003 both X-Men 2 and Hulk used biometric recognition technologies in the form of hand access control in X-Men 2 and fingerprint access in Hulk.
  • It wasn't however until 2004 when iRobot was released, starring American actor, Will Smith, that biometrics were truly showcased. The film set well into the future had some of the most advanced technologies on show, many of which hadn't, and still have not been developed today. The usage however of voice and palm recognition in the film cemented the futuristic look of the film in the audiences' mind, and both of which are in constant use today for securing buildings or sensitive data, these though just being two of many applications.
  • In 2005 the film The Island was released. Twice in the film clones use biometrics as a way of entering a house and starting a car.
  • The movie Gattaca portrays a society in which there are two classes of people: those genetically engineered to be superior (termed "Valid") and the inferior natural humans ("Invalid"). People considered "Valid" have greater privileges, and access to areas restricted to such persons is controlled by automated biometric scanners similar in appearance to fingerprint scanners, but which prick the finger and sample DNA from the resulting blood droplet.
  • The television program MythBusters attempted to break into a commercial security door[specify] equipped with biometric authentication as well as a personal laptop so equipped. While the laptop's system proved more difficult to bypass, the advanced commercial security door with "live" sensing was fooled with a printed scan of a fingerprint after it had been licked.


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