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Introduction to Biometrics Anil K. Jain • Arun A. Ross • Karthik Nandakumar Introduction to Biometrics Foreword by James Wayman Prof. Anil K. Jain Dr. Arun A. Ross Department of Computer Science Lane Department of Computer Science and Engineering and Electrical Engineering Michigan State University West Virginia University East Lansing, Michigan Morgantown, West Virginia USA USA [email protected] [email protected] Dr. Karthik Nandakumar Institute for Infocomm Research A*STAR Fusionopolis Singapore [email protected] ISBN 978-0-387-77325-4 e-ISBN 978-0- 387-77326-1 DOI 10.1007/978-0-387-77326-1 Springer New York Dordrecht Heidelberg London Library of Congress Control Number: 2011942231 © Springer Science+Business Media, LLC 2011 All rights reserved. This work may not be translated or copied in whole or in part without the written permission of the publisher (Springer Science+Business Media, LLC, 233 Spring Street, New York, NY 10013, USA), except for brief excerpts in connection with reviews or scholarly analysis. Use in connection with any form of information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is forbidden. The use in this publication of trade names, trademarks, service marks, and similar terms, even if they are not identified as such, is not to be taken as an expression of opinion as to whether or not they are subject to proprietary rights. Printed on acid-free paper Springer is part of Springer Science+Business Media (www.springer.com) Foreword In the 1901debutissue of the journalBiometrika, foundersof which includedSir Francis Galton and Karl Pierson, there appears an introductory editorial entitled, “SpiritofBiometrika”. It is almost impossible to study any type of life without being impressed by the small im- portanceoftheindividual.Inmostcasesthenumberofindividualsisenormous,theyarespread overwideareas,andhaveexistedthroughlongperiods.Evolutionmustdependuponsubstantial changesinconsiderablenumbersanditstheorythereforebelongstothatclassofphenomenawhich statisticianshavegrownaccustomedtorefertoasmass-phenomena.Asingleindividualmayhave avariationwhichfitsittosurvive,butunlessthatvariationappearsinmanyindividuals,orunless thatindividualincreases andmultiplieswithoutlossoftheuseful variationuptocomparatively greatnumbers-shortly,untilthefittypeoflifebecomesamass-phenomenon,itcannotbeaneffec- tivefactorinevolution. In the first partof the 20th century,“biometrics” was aboutbringingstatistical methodsintotherelativelynewandrapidlydevelopingfieldofevolutionarybiology so asto increaseknowledgeaboutvariancebetweenand withinlargepopulations. “Biometrics”wasaboutthestatisticalunderstandingofmass-phenomenon. Sometime around 1980, the term “biometrics”, by then well-established in the meaningof“activepursuitofbiologicalknowledgebyquantitativemethods”,was appropriatedas a designator for what had previouslybeen called “automated per- sonalidentification”(API).By1980,thefieldofAPIencompassedsuchtechnolo- giesasfingerprint,retina,voice,signature,faceandfinger-lengthrecognitionused for the purpose of differentiating individual humans. This use of the term “biometrics” in the narrower meaning of API turned the “Spirit of Biometrika” on its head:theindividualisnotof“smallimportance”asasingledatapointina“mass- phenomenon”,but is of all importance – a recognizable and unique entity distin- guishablefromthemassandaddressableasaperson.Biometricsinthissenseisnot aboutunderstandingmass-phenomenonwithinthecontextofevolutionarybiology, v vi Foreword butaboutunderstandingthedistinguishingcharacteristicsofindividualpersonsfor thepurposeofrecognition. Introduction to Biometrics by Anil Jain, Arun Ross and Karthik Nandakumar uses the term “biometrics”, in this more recent sense of individualization:the au- tomatedrecognitionofhumanindividualsbasedontheirbiologicalandbehavioral traits. Thisapplication,ofcourse,is immediatelypersonal.Itis aboutrecognizing (re again;cognoscere know/learn)meandyouandeachofthosearoundus.This recognitionoccursautomatically,meaningbycomputers,sothis“me”-directedout- come is being delivered almost immediately by impersonal machines, capable of bothproperoperationandimpropererrors.Therefore,biometricsinthisnewmean- inginvolvesmorethanpopulationstatisticsandbiology,butnowencompassescom- puterscience,computervision,patternrecognition,law,sociology,humanfactors, philosophyandevenreligion. In the 21st century, we now have these machines capable of quickly and ef- ficiently recognizing individuals, even when “the number of individuals is enor- mous”,andlinkingeachofthemto personaldata.Itisnowonderthattheinterest in biometric technologieshas grownrapidly over the last 10 years, particularlyin facilitation of international travel. But interest in itself is insufficient; advancing thesetechnologiesrequiresunderstandingbasedonanalysisofrealdata.Additional research continues to be needed to explore the privacy, legal, and security impli- cations of these technologiesand increase their usability, reliability and accuracy. Moreimportantly,weneedtoopendiscussiononwhichsocially-positive,security and privacy enhancing applications should be created and to ensure that biomet- rictechnologiesareusedtoempowerindividualsandnotenslavethem.Ofcourse, carefulconsiderationofthesecross-disciplinaryissuesrequiresacomprehensiveex- plicationofthetechnologies,theircapabilitiesandtheirrisks,whichleadsdirectly totheneedforthistextbook. IntroductiontoBiometricstakesacomprehensivelookatthecurrentmajorforms ofautomatedpersonalidentification,withparticularemphasisonfingerprint,face, andirisrecognition,inthecontextofhowthetechnologiesarebeingandshouldbe used:toensureindividualsecurityandprivacy.Thisbookfillsapedagogicalgapin the literature, supplying a unified treatment of technologies, developedseparately from different historical requirements, by emphasizing their algorithmic, system and application similarities. The approach of this textbook is very clearly techni- cal, with emphasison the patternmatchingalgorithmsemployedby the computer tomakerecognitiondecisions.Thisbookengagestechnically-capablestudentswho mayhavelimitedornoknowledgeaboutbiometricsandthusfacilitatesthegenera- tionofamoreknowledgeableworkforce.Thetextwillalsobeavaluablereference forthosealreadyactiveinthe field.Aswith previousbooksbythese authors,itis destinedtobecomeaclassic. July2011 JamesWayman Preface A number of crucial societal applications like international border crossing, elec- troniccommerce,andwelfaredisbursementrequirereliablepersonrecognitionsys- tems. Traditional person authentication methods based on passwords and identity documents often fail to meet the stringent security and performance demands of theseapplications,whichinturnhasspurredactiveresearchinthefieldofbiometric recognition.Biometricrecognition,orsimplybiometrics,isthescienceofestablish- ingtheidentityofapersonbasedonphysicalorbehavioralattributessuchasfinger- print, face, iris, and voice. Biometric systems are based on the premise that many ofthephysicalorbehavioralattributesofhumanscanbeuniquelyassociatedwith an individual. By capturing these attributes using appropriately designed sensors, representingtheminadigitalformat,andcomparingthisrecordeddataagainstthe dataacquiredfromthesamepersonatanearliertimeinstance,itispossibletoauto- matetheprocessofpersonrecognition.Thus,biometricrecognitioncanbeviewed asapatternrecognitionproblem,wherethemachinelearnsthesalientfeatures(pat- terns)inthebiometricattributesofanindividualandrobustlymatchessuchpatterns efficientlyandeffectively. While biometric characteristicssuch as fingerprintshave a long and successful historyinforensics,thedevelopmentofautomatedbiometricsystemsstartedonlyin thelaterhalfofthe20thcentury.However,thedeploymentofbiometricsystemshas beengainingmomentumoverthelasttwodecadesinbothpublicandprivatesectors. Thesedevelopmentshavebeenfueledinpartbyrecentgovernmentmandatesstip- ulatingtheuseofbiometricsforensuringreliabledeliveryofvariousservices.For example,theEnhancedBorderSecurityandVisaEntryReformActof2002enacted bytheUnitedStatesCongressmandatedtheuseofbiometricsintheissue ofU.S. visas. This led to the US-VISIT program (United States Visitor and Immigration StatusIndicatorTechnology)thatvalidatesthetraveldocumentsofforeignvisitors totheUnitedStatesbasedonfingerprints.TheInternationalCivilAviationOrgani- zation(ICAO)hasunanimouslyrecommendedthatitsmemberStatesuseMachine Readable Travel Documents(MRTDs) that incorporateat least the face biometric (some combination of face, fingerprint and iris can also be used) for purposes of verifyingtheidentityofapassportholder.TheGovernmentofIndiahasestablished vii viii Preface the Unique Identification Authority of India (UIDAI) to implement a nationwide biometricinfrastructuretocombatidentityfraudandprovideaccesstosocialbene- fitsfortheunderprivileged.ItplanstoissueeachresidentofIndiaaunique12-digit identificationnumbercalledAadhaarthatwillbebasedon10fingerprintsandtwo irides.Thus,itisclearthatbiometrictechnologyhasthepotentialtoprofoundlyin- fluencethewaysinwhichwearerecognizedforconductingvarioustransactionson adailybasis. Objectives Despite its rapid proliferation,the study of biometric technologyhas mostly been restricted to a fairly small community of biometric researchers and practitioners due to two reasons. Firstly, biometric recognition is often considered as a rather specialized field and is typically taught only as part of a course on pattern recognition, computer vision, or image processing. However, it is important to realize that biometric recognition is a broad and importantsubject in its own right; chal- lenges and issues involved in the design of biometric systems go beyond pattern recognitionand encompassesa variety of other topics includingapplied statistics, sensor design, software engineering, information theory, and human factors. Sec- ondly, knowledgeabout biometric technologiesis primarily contained in research articles and books written for the research community, which are accessible only to thosewitha priorintroductiontothisfield.In short,thereis nobiometricbook thatcaterstoundergraduateandgraduatestudentswhomaynothaveanextensive backgroundinbiometrics.Sincethisisthefirsttextbookonbiometrics,ourprimary objectivesareto: • provide an introductionto the basic concepts and methodologiesfor biometric recognition;and • build a foundation that can be used as the basis for more in-depth study and researchonthistopic. Tofulfiltheseobjectives,wefocusonlyonkeyillustrativetechniquesthatarewidely used in the biometricscommunity,ratherthanprovidinga detailedanalysisofthe state-of-the-artadvancements.Ourfocusisprimarilyonthreemostcommonlyused traits,namely,fingerprint,face,andiris,althoughwediscussafewotherbiometric traitsbriefly. Organization • Chapter1introducesthegenericconceptsinbiometricrecognition,includingan overview of how a biometric system works, the terminology used to describe biometrictraitsandsystems,thewaysinwhichabiometricsystemcanbeused, Preface ix thefactorsaffectingthedesignofabiometricsystem,andthemeasurestoeval- uatetheperformanceofabiometricsystem.Chapters2,3,and4discusshowa biometricsystemcanbeimplementedbasedonfingerprint,face,andirischarac- teristicsofaperson,respectively.Thesethreechaptersshareacommonstructure. Thesensing,featureextraction,andmatchingtechniquesforthesethreebiomet- ricidentifiersareintroducedinorder,followedbyadiscussiononadvancedtop- icsthatarespecifictoeachidentifier. • Chapter2onfingerprintsfocusesmoreontheminutiae-basedrepresentationand matchingalgorithms. This chapter also includesdetails on topics like indexing largefingerprintdatabases,generationofartificial(synthetic)fingerprintimages, andpalmprint-basedbiometricrecognition. • Chapter3emphasizestheproblemoffacedetectionandthedifferentapproaches for matching 2-dimensionalface photographs.Other issues in face recognition suchashandlingpose,illumination,andexpressionvariations,matchingofhet- erogeneousfaceimages,andfacemodelingarealsocoveredinthischapter. • Chapter 4 deals with the problem of iris segmentation in detail, followed by a descriptionof iris encodingandmatchingbasedon Gaborwavelets. Quality of theirisimageisacriticalissueinirisrecognition,andtechniquesforestimating theirisimagequalityarealsodiscussedinChapter4. • Chapter5brieflydescribesthetechniquesforpersonrecognitionbasedonaddi- tionalbiometricattributeslikehandgeometry,ear,andgait.Softbiometricchar- acteristicslikescars,marks,tattoos,andperiocularbiometricsarealsousefulin identifyingapersoninsomescenarios.Thechapterconcludeswithadiscussion onhowthesesoftbiometricidentifierscanbeusedinpersonrecognition. • High-security applications and large-scale civilian identification systems place stringentaccuracyrequirementsthatcannotbemetbybiometricsystemsbased onasinglebiometricidentifier.Multibiometricsystemsovercomethislimitation byintelligentlycombiningtheevidencefrommultiplebiometricsources.Adis- cussiononthetaxonomyofsuchmultibiometricsystemsandthedifferentways inwhichtheinformationfrommultiplesourcescanbefusedtoobtainareliable identitydecisionistheprimaryfocusofChapter6. • Finally,thecommonsecurityvulnerabilitiesof a biometricsystem andthe var- iouscountermeasuresthatneed to be followedto addressthese threatsare pre- sentedinChapter7.Inparticular,thischapteremphasizestwoofthemostwell- studied vulnerabilitiesof a biometric system, namely, spoof detection and bio- metrictemplatesecurity. Thewebsiteforthebookwillbeinitiallymaintainedathttp://www.csee. wvu.edu/˜ross/BiometricsTextBook. Homework assignments, reading resources,samplecodes,linkstobiometricdatabases,anderratawillbedocumented inthiswebsite.Thiswebsitewillbeupdatedregularlyforthebenefitofthereader.

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Biometric recognition, or simply biometrics, is the science of establishing the identity of a person based on physical or behavioral attributes. It is a rapidly evolving field with applications ranging from securely accessing one’s computer to gaining entry into a country. While the deployment of