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Biometric Terms: Glossary

Active Impostor Acceptance
When an impostor submits a modified, simulated or reproduced biometric sample, intentionally attempting to relate it to another person who is an enrollee, and is incorrectly identified or verified by a biometric system as being that enrollee.

Application Developer
An individual entrusted with developing and implementing a biometric application.

The submission of a biometric sample to a biometric system for identification or verification. A biometric system may allow more than one attempt to identify or verify.

The process of comparing a submitted biometric sample against the biometric reference template of a single enrollee whose identity is being claimed, to determine whether it matches the enrollee's template. Contrast with 'Identification.' The preferred biometric term is 'Verification.'

Automatic ID/Auto ID
An umbrella term for any biometric system or other security technology that uses automatic means to check identity. This applies to both one-to-one verification and one-to-many identification.

Behavioral Biometric
A biometric which is characterized by a behavioral trait that is learned and acquired over time rather than a physiological characteristic.

A measurable, physical characteristic or personal behavioral trait used to recognize the identity, or verify the claimed identity, of an enrollee.

Biometric Application
The use to which a biometric system is put. See also 'Application Developer.'

Biometric Data
The extracted information taken from the biometric sample and used either to build a reference template or to compare against a previously created reference template.

Biometric Engine
The software element of the biometric system which processes biometric data during the stages of enrolment and capture, extraction, comparison and matching.

Biometric Identification Device

The preferred term is 'Biometric System.'

Biometric Sample
Data representing a biometric characteristic of an end-user as captured by a biometric system.

Biometric System
An automated system capable of: capturing a biometric sample from an end user; extracting biometric data from that sample; comparing the biometric data with that contained in one or more reference templates; deciding how well they match; and indicating whether or not an identification or verification of identity has been achieved.

Biometric Taxonomy
A method of classifying biometrics. For example, San Jose State University's (SJSU) biometric taxonomy uses partitions to classify the role of biometrics within a given biometric application. An application may be classified as:

  • Cooperative vs. Non-Cooperative User
  • Overt vs. Covert Biometric System
  • Habituated vs. Non-Habituated User
  • Supervised vs. Unsupervised User
  • Standard Environment vs. Non Standard Environment

Biometric Technology
A classification of a biometric system by the type of biometric.

The method of taking a biometric sample from the end user.

The process of testing a biometric system to ensure that it meets certain performance criteria. Systems that meet the testing criteria are said to have passed and are certified by the testing organization.

The process of comparing a biometric sample with a previously stored reference template or templates. See also 'One-To-Many' and 'One-To-One.'

Claim of Identity
When a biometric sample is submitted to a biometric system to verify a claimed identity.

A person submitting a biometric sample for verification or identification whilst claiming a legitimate or false identity.

Closed-Set Identification
When an unidentified end-user is known to be enrolled in the biometric system. Opposite of 'Open-Set Identification.'

Crossover Rate
Synonym for 'Equal Error Rate.'

D Prime
A statistical measure of how well a biometric system can discriminate between different individuals. The larger the D Prime value, the better a biometric system is at discriminating between individuals.

Degrees of Freedom
The number of statistically independent features in biometric data.

Discriminant Training
A means of refining the extraction algorithm so that biometric data from different individuals are as distinct as possible.

End User
A person who interacts with a biometric system to enroll or have his/her identity checked.

End User Adaptation
The process of adjustment whereby a participant in a test becomes familiar with what is required and alters their responses accordingly.

A person who has a biometric reference template on file.

The process of collecting biometric samples from a person and the subsequent preparation and storage of biometric reference templates representing that person's identity.

Enrollment Time
The time period a person must spend to have his/her biometric reference template successfully created.

Equal Error Rate
When the decision threshold of a system is set so that the proportion of false rejections will be approximately equal to the proportion of false acceptances. A synonym is 'Crossover Rate.'

The process of converting a captured biometric sample into biometric data so that it can be compared to a reference template.

Failure to Acquire
Failure of a biometric system to capture and extract biometric data.

Failure to Acquire Rate
The frequency of a failure to acquire.

False Acceptance
When a biometric system incorrectly identifies an individual or incorrectly verifies an impostor against a claimed identity. Also known as a Type II error.

False Acceptance Rate/FAR
The probability that a biometric system will incorrectly identify an individual or will fail to reject an impostor. Also known as the Type II error rate. It is stated as follows:
where FAR is the false acceptance rate
NFA is the number of false acceptances
NIIA is the number of impostor identification attempts
NIVA is the number of impostor verification attempts

False Match Rate
Alternative to 'False Acceptance Rate'. Used to avoid confusion in applications that reject the claimant if their biometric data matches that of an enrollee. In such applications, the concepts of acceptance and rejection are reversed, thus reversing the meaning of 'False Acceptance' and 'False Rejection.' See also 'False Non-Match Rate.'

False Non-Match Rate
Alternative to 'False Rejection Rate'. Used to avoid confusion in applications that reject the claimant if their biometric data matches that of an enrollee. In such applications, the concepts of acceptance and rejection are reversed, thus reversing the meaning of 'False Acceptance' and 'False Rejection.' See also 'False Match Rate.'

False Rejection
When a biometric system fails to identify an enrollee or fails to verify the legitimate claimed identity of an enrollee. Also known as a Type I error.

False Rejection Rate/FRR
The probability that a biometric system will fail to identify an enrollee, or verify the legitimate claimed identity of an enrollee. Also known as a Type I error rate. It is stated as follows:
where FRR is the false rejection rate
NFR is the number of false rejections
NEIA is the number of enrollee identification attempts
NEVA is the number of enrollee verification attempts

Field Test
A trial of a biometric application in 'real world,' as opposed to laboratory, conditions.

Biometric system end users whose pattern of activity when interfacing with the system varies beyond the specified range allowed by the system, and who consequently may be falsely rejected by the system.

Genetic Penetrance
The degree to which characteristics are passed from generation to generation.

The one-to-many process of comparing a submitted biometric sample against all of the biometric reference templates on file to determine whether it matches any of the templates and, if so, the identity of the enrollee whose template was matched. The biometric system using the one-to-many approach is seeking to find an identity amongst a database rather than verify a claimed identity. Contrast with 'Verification.'

A person who submits a biometric sample in either an intentional or inadvertent attempt to pass him/herself off as another person who is an enrollee.

In-House Test

A test carried out entirely within the environs of the biometric developer which may or may not involve external user participation.

Live Capture

The process of capturing a biometric sample by an interaction between an end user and a biometric system.

The process of comparing a biometric sample against a previously stored template and scoring the level of similarity. An accept or reject decision is then based upon whether this score exceeds the given threshold.

Synonym for 'Identification.'

Synonym for 'Verification.'

Open-Set Identification
Identification, when it is possible that the individual is not enrolled in the biometric system. Opposite of 'Closed-Set Identification.'

Out Of Set
In open-set identification, when the individual is not enrolled in the biometric system.

Passive Impostor Acceptance

When an impostor submits his/her own biometric sample and claiming the identity of another person (either intentionally or inadvertently) he/she is incorrectly identified or verified by a biometric system. Compare with 'Active Impostor Acceptance.'

Performance Criteria
Pre-determined criteria established to evaluate the performance of the biometric system under test.

Physical/Physiological Biometric
A biometric which is characterized by a physical characteristic rather than a behavioral trait.

Receiver Operating Curves
A graph showing how the false rejection rate and false acceptance rate vary according to the threshold.

The preferred term is 'Identification'.

Response Time
The time period required by a biometric system to return a decision on identification or verification of a biometric sample.

Template/Reference Template
Data which represents the biometric measurement of an enrollee used by a biometric system for comparison against subsequently submitted biometric samples.

Third Party Test
An objective test, independent of a biometric vendor, usually carried out entirely within a test laboratory in controlled environmental conditions.

Threshold/Decision Threshold
The acceptance or rejection of biometric data is dependent on the match score falling above or below the threshold. The threshold is adjustable so that the biometric system can be more or less strict, depending on the requirements of any given biometric application.

Throughput Rate
The number of end users that a biometric system can process within a stated time interval.

Type I Error
See 'False Rejection.'

Type II Error
See 'False Acceptance.'

The client to any biometric vendor. The user must be differentiated from the end user and is responsible for managing and implementing the biometric application rather than actually interacting with the biometric system.

The process of demonstrating that the system under consideration meets in all respects the specification of that system.

The process of comparing a submitted biometric sample against the biometric reference template of a single enrollee whose identity is being claimed, to determine whether it matches the enrollee's template. Contrast with 'Identification.'

Zero Effort Forgery
An arbitrary attack on a specific enrollee identity in which the impostor masquerades as the claimed enrollee using his or her own biometric sample.

Read more about it at:
> This glossary was adapted from Resonance Publications, who kindly contributed the content.
This was last updated in May 2008

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