Q. What are the requirements for a biometric characteristic?

In the development of biometric identification systems, physical and behavioral characteristics for recognition are required
  • which dispose of biometric features which are as unique as possible, i.e., which do not reappear at any other person: Uniqueness
  • which occur in as many people as possible: Universality
  • whose biometric features don't change over time: Permanence
  • which are measurable with simple technical instruments: Measurability
  • which are easy and comfortable to measure: User friendliness

Q. What are the most well known biometric characteristics?

Biometric characteristic Description of the features
Fingerprint Finger lines, pore structure
Signature (dynamic) Writing with pressure and speed differentials
Facial geometry Distance of specific facial features (eyes, nose, mouth)
Iris Iris pattern
Retina Eye background (pattern of the vein structure)
Hand geometry Measurement of fingers and palm
Finger geometry Finger measurement
Vein structure of hand Vein structure of the back or palm of the hand or a finger
Ear form Dimensions of the visible ear
Voice Tone or timbre
DNA DNA code as the carrier of human hereditary
Odor Chemical composition of the one's odor
Keyboard strokes Rhythm of keyboard strokes (PC or other keyboard)

Q. What factors contribute to a biometric characteristic's development?

Biometric characteristics develop:
  • through genetics: genotypic
  • through random variations in the early phases of an embryo's development: randotypic (often called phenotypic)
  • or through training: behavioral
As a rule, all three factors contribute to a biometric characteristic's development, although to varying degrees. The following table rates the relative importance of each factor (o is small, ooo is large):
Biometric characteristic

genotypic*

randotypic*

behavioral**

Fingerprint (only minutia)

o

ooo

o

Signature (dynamic)

oo

o

ooo

Facial geometry

ooo

o

o

Iris pattern

o

ooo

o

Retina (Vein structure)

o

ooo

o

Hand geometry

ooo

o

o

Finger geometry

ooo

o

o

Vein structure of the hand

o

ooo

o

Ear form

ooo

o

o

Voice (Tone)

ooo

o

oo

DNA

ooo

o

o

Odor

ooo

o

o

Keyboard Strokes

o

o

ooo

Comparison: Password

(ooo)

* Randotypic patterns often show genotypic traits in their overall structure. These genotypic traits may disappear with increasing refinement (e.g., development of branches on a tree). ** Most implementations react to learn effects to various degrees, and therefore do have behavioral contributions which cannot be neglected.

Q. How does the manner of formation influence the usefulness of biometric characteristics?

Even though the type of developmental factor does not solely determine a biometric characteristic's usefulness, there are a few things to take into account:
  • pure genotypic characteristics can't differentiate between monozygotic (identical) twins or clones
  • purely behavioral characteristics are, by definition, easiest to imitate
  • behavioral characteristics are strongly affected by external influences and the disposition of the user
  • normally for identification purposes, randotypic contributions are essential due to their necessity for creating absolute uniqueness

Q. How does one recognize randotypic characteristics?

The following must be considered:
  • Even monozygotic twins have obviously differing randotypic characteristics.
  • As a rule of thumb, random variations do NOT follow bodily symmetry. For example, the right and left iris have different details, and are not mirror symmetrical to each other.

Q. Which biometric characteristics are most constant over time?

Reasons for variation over time:
  • Growth
  • Wear and tear
  • Aging
  • Dirt and grime
  • Injury and subsequent regeneration
  • etc.
Biometric characteristics, which are minimally affected by such variation are preferred. The degree to which this is possible is shown in the following table. Easily changed effects such as dirt and quickly healing injuries such as an abrasion, are not taken into consideration.
Biometric characteristic Permanence over time
Fingerprint (Minutia) oooooo
Signature (dynamic) oooo
Facial structure ooooo
Iris pattern ooooooooo
Retina oooooooo
Hand geometry ooooooo
Finger geometry ooooooo
Vein structure of the hand oooooo
Ear form oooooo
Voice (Tone) ooo
DNA ooooooooo
Odor oooooo?
Keyboard strokes oooo
Comparison: Password ooooo

Q. Which biometric characteristics are most suitable for recognition purposes?

Prior to comparing the relative worth of different biometric characteristics, we must define the appropriate criteria to be used. For these purposes, we will use four categories:
  • Comfort: duration of verification and the ease of use
  • Accuracy: minimal error rates (clarity, consistency, measurability)
  • Availability: the portion of a potential user group who can use biometrics for technical recognition purposes (universal, measurable)
  • Costs: essentially due to the biometric capture device incl. sensors.
  • Note that some of the following ratings are based on current versions (status: March 2000) which could change drastically with new solutions.
Biometric characteristic

Comfort

Accuracy

Availability

Costs

Fingerprint ooooooo ooooooo oooo ooo
Signature (dynamic) ooo oooo ooooo oooo
Facial geometry ooooooooo oooo ooooooo ooooo
Iris oooooooo ooooooooo oooooooo oooooooo
Retina oooooo oooooooo ooooo ooooooo
Hand geometry oooooo ooooo oooooo ooooo
Finger geometry ooooooo ooo ooooooo oooo
Vein Structure of the hand oooooo oooooo oooooo ooooo
Ear form ooooo oooo ooooooo ooooo
Voice oooo oo ooo oo
DNA o ooooooo ooooooooo ooooooooo
Odor ? oo ooooooo ?
Keyboard strokes oooo o oo o
Comparison: Password ooooo oo oooooooo o

green = best red = worst

As one can see, determining an 'optimal' biometric characteristic is hardly possible. For biometric characteristics ranking high in accuracy, fingerprints currently have the lowest costs. The iris rates high in all categories, unfortunately including cost. If the costs would sink significantly, the iris would be ideal. DNA loses points in accuracy, because it can't differentiate between monozygotic twins today.

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