a biometric is a unique, measurable characteristic or ...jordi/biometvisio.pdf · sistemes...

Sistemes BiomètricsSistemes Biomètrics 1Jordi Vitrià, Centre de Visió per Computador, Maig 1999

Definition

A biometric is a unique, measurablecharacteristic or trait of a humanbeing for automatically recognizing orverifying identity.

è Physical biometrics: iris, retina, face, finger,hand, voice

è Behavioral biometrics: signature, typingrhythm


Levels of security•Lowest: Something that you have, such an ID badge with a photograph on it.

• Middle: Something that you know, such as a password to access a computeror a Personal Identification Number (PIN) to access funds at a bank tellermachine.

• Highest: Something that you do and something which you are (biometrics).

History•Finger images ® ancient China

• Signature - …

• 1970-1980 - Identimat (hand shape, finger length)

• 60’s-70’s - Fingerscan technologies

• 1985 - Retina

• 70’s - Speaker verification

• 80’s - Signature and face


How Biometrics WorkThe procedure

1. The system captures a (number of) sample(s) of the biometric characteristicduring an enrollment process.

2. Unique features are extracted and converted by the system into amathematical code.

3. The sample is stored as the biometric template for that person. The templatemay reside in the biometric system itself, or in any other form of memorystorage, such as a computer database, a smart card or a bar-code.

4. There may be a trigger, or a means of tying the template to the person (i.e. aPIN).

5. The user interacts with the biometric system for a second time to have his orher identity checked.

6. A new biometric sample is taken. This is compared to the template.

7. If the template and he new sample match, the end user is granted access.


Identification/Recognition andVerification

Who is this?Is this person who he says he is?

Identification/Recognition: a sample is presented tothe biometric system during enrollment. The systemthen attempts to find out who the sample belongs to, bycomparing the sample with a database of samples.

Verification is a one to one process, where thebiometric system is seeking to verify identity. Here asingle biometric sample is matched against anothersample. Is this person who he says he is?


PROPERTIES OF CHARACTERISATION

THE ACCURACY of biometric identification method is stated in terms of:

• False acceptance rate (FAR): The percentage ofunauthorised persons accepted in error.

• False rejection rate (FRR): The percentage of authorisedpersons who are incorrectly denied acceptance.

These performance criteria are not easily interpreted, because there are several factors thatcan influence them:

First there is a relationship between these two performance criteria. Oftenthere exists some parameter that can be adjusted in order to decrease theFRR and increase FAR or vice versa.

FAR/FRR figures can be determined with "one-try" or "three-try" testprotocols. In a "one-try" test protocol, people are given only one chance totest their biometric data. After that, they are accepted or rejected. In a"three-try" test protocol they have up to three chances before they arereally rejected. If consecutive measurements are statistically independentthis improves the false rejection rate without really deteriorating the falseacceptance rate. However, for some applications the three tries testprotocol may not be acceptable.


Technology OverviewThis section looks at the operation of each biometrictechnology within the four stages of capture, extraction,comparison and matching.

1. Eye1.1 Iris1.2 Retina

2. Face3. Fingerscanning

3.1 Finger Image Verification3.2 Finger Image Identification

4. Hand Geometry5. Finger Geometry6. Palm


Technology Overview: Eye - IrisThe iris is the colored ring of textured tissue thatsurrounds the pupil of the eye.

è Each iris is a unique structure, featuring a complex pattern.This can be a combination of specific characteristics known ascorona, crypts, filaments, frekles, pits, radial furrows andstriations.


Technology Overview: Eye - Iris

Capture - A black and white video camera captures an image of the iris.This should be done in a well-lit environment. Contact lenses do not interferewith image capture. Sunglasses and glasses, however, should not be worn asthese can affect the capture process.


Technology Overview: Eye - Iris


Technology Overview: Eye - IrisProbability of two irises producing the same code: 1 in 1078

Independent variables (degrees-of-freedom) extracted: 266

IrisCode size (uncompressed): 512 bytes

Information density of IrisCodes (human population entropy): 3.4 bitsper square millimeter of iris

Achievable accuracy: Cross-over error rate: 1 in 1,200,000(Cross-over error rate is measured at a decision criterion that produces equal rates of false accept and falsereject.)

Average Recognition speed (database of 100,000 IrisCodes):Identification (exhaustive or one-to-many search): 2 secondsVerification (matching file or one-to-one search with PIN entry): 3 seconds

Database limitations: There are no operating limits on the size of thedatabase. Very large databases will require appropriate memory and processingdesign options.

Hardware compatibility: IriScan's iris recognition software is designed tofunction using a variety of image acquisition (camera) platforms and PC-basedprocessors.

Operating systems compatibility: DOS and Windows (NT/95)


Technology Overview:Eye - RetinaThe retina is the layer of blood vesselssituated at the back of the eye. Retinabiometrics are regarded as the motsecure biometric method. A preciseenrollment process is necessary,which involves lining up the eye toachieve an optimum reading.Capture - The eye is positioned in front of the system,approximately three inches from an eyepiece. The enduser must look at a green dot for a few seconds, viewedthrough the eyepiece. When this is done, the eye issufficiently focused for the scanner to capture the retinapattern. The fovea is scanned and the pattern of vesselscaptured.

Extraction - The biometric system maps out the positionof the blood vessels

Comparison - One-to-many identification is usuallyperformed.

False rejection rate: 12.4 percent (one-try) 0.4 per cent(three-try);False acceptance rate: 0 Nofalse acceptances;Vulnerability to fraud: Nocounterfeits seem possible. Falseeyes, contact lenses and eye;transplants cannot breach thesecurity of this device;Ease of use: Difficult to use.Socially difficult to accept becausepeople do not like to have theireyes scanned;Suitable for everyone: Suitablefor everyone with eyes;Speed of identification: 1.5seconds;Size for storage ofidentification tokens: 40 bytes;Long term stability: The retinalvascular pattern is very stable.Only a small number of diseasesor injuries will change thispattern;Proven technology: Used in afair amount of systems.


Technology Overview: Face

The face is a key component in the way humans beingsremember and recognize each other.

Capture - Standard video techniques use a facial image,or collections of images, captured by a video camera.The precise position of user face and the surroundinglighting conditions can affect the system’s performance.

Extraction - The biometric system converts the facialimage into a pattern an then a unique code.

Comparison - One-to-one verification is the mostcommond method of comparison.


Technology Overview:Fingerscanning

Most one-to-one and one-to-many fingerscan systemsanalyze small unique marks onthe finger image - which areknown as minutiae. These maybe defined as ridge endings, orbifurcations.

Other fingerscan systemsanalyze tiny sweat pores on thefinger which, in the same way asminutiae, are uniquelypositioned. Finger image densityor distance between ridges mayalso be analyzed.


Technology Overview: Fingerscanning

è Certain conditions may affect the prints of differentindividuals. Dirty, dry or cracked prints can affectquality; age, gender or ethnic background are alsofound to have impact on the quality of finger images.

è The way a user interacts with a finger scan is anotherimportant consideration (pressing to hard..)

è One-to-one systems use four main capturetechniques: optical, thermal or tactile, capacitance andultrasound.

è One-to-many products capture finger images usingthe optical technique or by electronically scanningimages from paper.


Technology Overview: Finger ImageVerification



Ridge Defined as havingdouble the distance fromstarting to ending, asneighboring ridges are wide

Evading Ends Two ridgeswith different directions runparallel with each other formore than 3mm.

Bifurcation A ridge splits,both ridges maintain thesame direction and arelonger than 3mm

Hook A ridge splits; oneridge is not longer than3mm

Fork Two ridges areconnected by a third ridgenot longer than 3mm

Dot The ridge section is nolonger than the neighboringridges are wide

Eye The ridge splits and rejoinswithin 3mm

Island A ridge splits and joinsagain within not less than 3mmand not more than 6mm. Theenclosed area is ridgeless.

Enclosed Ridge A ridge notlonger than 6mm between twoother ridges

Enclosed Loop A non-patterndetermining loop between two ormore parallel ridges.

Specialties Rare ridge forms suchas question marks and butcherhooks


Technology Overview: Hand Geometry

Hand geometry takes a three dimensional image of thehand and measures the shape and length of fingers andknuckles. Although hand geometry does not achieve thehighest levels of accuracy, it is convenient to use andthe primary advantage is that large volumes of userscan be processed quickly.

Capture - A user places a hand on the hand reader,aligning fingers with specially positioned guides. Acamera, positioned above the hand captures an image.

Extraction - Three dimensional measurements ofselected points on the hand are taken.

Comparison - Hand geometry is used for one-to-oneidentification.


Technology Overview: Hand Geometry


Technology Overview: Finger GeometryFinger geometry, or the measurement of finger shape, usesthe same principle as hand geometry. Measurements of uniquefinger characteristics, such as finger width, length, thicknessand knuckle size are taken.

Capture - There are two techniques in the market. The firstmeasures the geometry of two or more fingers. A cameratakes a three-dimensional measurement when an end userplaces the index and middle finger, of either the right or lefthand, onto a reader. The second technique requires the userto insert the finger into a tunnel so that three dimensionalmeasurements of the finger can be taken.

Extraction - Three dimensional measurements of selectedpoints on the hand are taken.

Comparison - Finger geometry is used for one-to-oneidentification.


Technology Overview: Palm

Palm biometrics can be closely aligned with fingerprintscanning. Ridges, valleys and minutiae data are found on thepalm. This area of the biometrics is particularly focused on thelaw enforcement community, as latent palm images areequally as useful in crime detection as latent finger images.

Capture - The capture process is essentially the same as theoptical technique described above for fingerscanning. A palmsystem captures images when a hand is placed on a scanner.Latent or ink palm images can also be scanned.

Extraction - Minutiae data is extracted.

Comparison - Palm biometrics are predominantly used for one-to-many identification.

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