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.
There exist four main types of fingerprint reader hardware:
- 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.
- 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.
- 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.
- 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:
- Minutiae matching relies on recognition of the minutiae points, this is the most widely used technique
- Pattern matching simply compares two images to see how similar they are, often used in fingerprint systems to detect duplicates