Fingerprint Recognition

Fingerprint recognition refers to the automated method of identifying or confirming the identity of an individual based on the comparisson of two fingerprints. Fingerprint recognition is one of the most well known biometrics, and it is by far the most used biometric solution for authentication on computerized systems. The reasons for fingerprint recognition being so popular are the ease of acquisition, established use and acceptance when compared to other biometrics, and the fact that there are numerous (ten) sources of this biometric on each individual.

 

fingerprint loop

Loop pattern

arch

Arch pattern

fingerprint whorl

Whorl pattern (all 3 pictures in public domain)

 

Fingerprint patterns

Basic patterns

The three basic patterns of fingerprint ridges are the arch, the loop, and the whorl. An arch is a pattern where the ridge enters one side of the finger, then rises in the center forming an arch, and exits on the other side of the finger. With a loop the ridge enters one side of the finger, then forms a curve, and exits on the same side of the finger from which it entered. Loops are the most common pattern in fingerprints. Finally a whorl is the pattern you have when ridges form circularly around a central point.
Refer to the images on the right for examples of each pattern.

Minutiae features

Minutiae refer to specific points in a fingerprint, these are the small details in a fingerprint that are most important for fingerprint recognition.

There are three major types of minutiae features: the ridge ending, the bifurcation, and the dot (also called short ridge). The ridge ending is, as indicated by the name, the spot where a ridge ends. A bifurcation is the spot where a ridge splits into two ridges. Spots are those fingerprint ridges that are significantly shorter than other ridges.

Fingerprint readers

There exist four main types of fingerprint reader hardware:

  1. Optical readers are the most common type of fingerprint readers. The type of sensor in an optical reader is a digital camera that acquires a visual image of the fingerprint. Advantages are that optical readers start at very cheap prices. Disadvantages are that readings are impacted by dirty or marked fingers, and this type of fingerprint reader is easier to fool than others.
  2. Capacitive readers, also referred to as CMOS readers, do not read the fingerprint using light. Instead a CMOS reader uses capacitors and thus electrical current to form an image of the fingerprint. CMOS readers are more expensive than optical readers, although they still come relatively cheap with prices starting well below 100 euro’s.
    An important advantage of capacitive readers over optical readers is that a capacitive reader requires a real fingerprint shape rather than only a visual image. This makes CMOS readers harder to trick.
  3. Ultrasound readers are the most recent type of fingerprint readers, they use high frequency sound waves to penetrate the epidermal (outer) layer of the skin. They read the fingerprint on the dermal skin layer, which eliminates the need for a clean, unscarred surface. All other types of fingerprint readers acquire an image of the outer surface, thus requiring hands to be cleaned and free of scars before read-out. This type of fingerprint reader is far more expensive than the first two, however due to their accuracy and the fact that they are difficult to fool the ultrasound readers are already very popular.
  4. Thermal readers sense, on a contact surface, the difference of temperature in between fingerprint ridges and valleys. Thermal fingerprint readers have a number of disadvantages such as higher power consumption and a performance that depends on the environment temperature.
 

After a fingerprint image is acquired by the fingerprint reader hardware, this fingerprint must be interpreted. It must be processed in such a way that read-outs can be efficiently compared and matched against each other.

Generally speaking two types of matching software exist:

  1. Minutiae matching relies on recognition of the minutiae points, this is the most widely used technique
  2. Pattern matching simply compares two images to see how similar they are, often used in fingerprint systems to detect duplicates

Application of fingerprint recognition

Because it is one of the cheapest biometric solutions, fingerprint recognition already knows many different applications. We only list a few examples here:

  • Logical access control, for example there exist numerous fingerprint reader devices and softwares for access control to personal computers
  • Physical access control, for example locks with a fingerprint reader
  • Fingerprint attendance systems for time and attendance management
  • Biometric alternative to loyalty card systems

Suitability of fingerprint recognition

How suitable is fingerprint recognition as a biometric solution? We use the following 7 criteria to evaluate the suitability of fingerprint recognition:

Universality Only very few people miss all 10 fingers. Most fingerprint recognition software allows to enroll multiple fingers which avoids that an individual is no longer granted access after injury.
Uniqueness It is generally accepted that fingerprints are unique to an individual. However, there is a risk that fingerprints of two different individuals match if the fingerprint image is of insufficient quality. Therefore the False Acceptance Rate (FAR) is highly dependent on the quality of the fingerprint reader.
Permanence Fingerprints do not change with ageing, but as people age they lose collagen which makes their fingerprint harder to read and this can lead to significantly more false rejects with elderly people. Injuries, such as fire wounds, can damage a fingerprint but if multiple fingers are enrolled the likelihood of an authorized individual being denied access is reduced.
Collectability Fingerprints are easy to acquisition, the cheapest fingerprint readers available use a digital camera. Fingerprint readers that are more difficult to fool, such as CMOS readers, are even not overly expensive. In some environments, where for example people are unable to wash their hands, more expensive means might be necessary to acquire a useable fingerprint image.
Acceptability Fingerprints are easily accepted as soon as people reflect that they leave their fingerprints everywhere and that no sensitive information, such as medical conditions, can be derived from fingerprints.
Circumvention There are a number of concerns when using fingerprint recognition

  • A finger can be cut off, this is no joke it already happened. Fingerprint sensors with liveness detection can resolve this issue.
  • Fingerprint dummies are not too difficult to make, the effort is highly dependent of the biometric device to be fooled. Some of the cheapest devices can even be fooled by a fingerprint image that is printed on paper or transparency. Dummies can be created for each type of sensor, however in general the more complicated (and thus expensive) sensors are more difficult to fool. Liveness detection do make fingerprint readers a lot more difficult to fool.

Make a thorough analysis before implementing fingerprint recognition as a means for authentication or identification in a high security environment. Avoid using fingerprint readers without liveness detection.

Performance In terms of speed, accuracy and robustness the devices actually on the market should cover any need, except maybe for big corporations and government applications where matching algorithms might become a bottleneck.

False Acceptance Rate (FAR) and False Rejection Rate (FRR) are too dependent on the device, the software implementation and on how the system is used. Therefore we cannot generalize this.

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