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Nov 8, 2013 (4 years and 4 days ago)

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Biometric Fingerprin
t Identification

Dept. of EEE


MESCE, Kuttippuram

1


1. INTRODUCTION


Positive identification of individuals is a v
ery basic societal requirement.
Reliable user authentication is becoming an increasingly important task in the web


enabled world. The consequences of an insecure authentication system
in a

corporate or enterprise environment can be catastrophic, and may include loss of

confidential information, denial of service, and compromised data integrity. The

value
of reliable user authentication is not limited to just computer or network

access.
Many other applications in every day life also require user authentication,

such as
banking, e
-
commerce, and could benefit from enhanced security.



In fact, as more interactions take electronically, it becomes even more important
to have an elect
ronic verification of a person’s identity. Until recently, electronic
verification took one of two forms. It was based on something the person had in their
possession, like a magnetic swipe card, or something they knew, like a password. The
problem is, the
se forms of electronic identification are not very secure, because they can
be given away, taken away, or lost and motivated people have found ways to forge or
circumvent these credentials.



The ultimate form of electronic verification of a person’s is bi
ometrics.
Biometrics refers to the automatic identification of a person based on his/her
physiological or behavioral characteristics such as finger scan, retina, iris, voice scan,
signature scan etc. By using this technique physiological characteristics of

a person can
be changed into electronic processes that are inexpensive and easy to use. People have
always used the brain’s innate ability to recognize a familiar face and it has long been
known that a person’s fingerprints can be used for identification.

Biometric Fingerprin
t Identification

Dept. of EEE


MESCE, Kuttippuram

2


2. IDENTIFICATION AND VERIFICATION SYSTEMS

A person’s identity can be resolved in two ways: identification and
verification. The former involves identifying a person from all biometric measurements
collected in a database and this involves a one
-
to
-
many
match also referred to as ‘cold
search’. “Do I know who you are”? is the inherent question this process seeks to
answer. Verification involves authenticating a person’s claimed identity from his or her
previously enrolled pattern and this involves a one to

one match. The question it seeks
to answer is, “Are you claim to be?”


2.1 VERIFICATION

Verification involves comparing a person’s fingerprint to one that pass
previously recorded in the system database. The person claiming an identity provided a
fingerpr
int, typically by placing on a capacitance scanner or an optical scanner. The
computer locates the previous fingerprint by looking at the person’s identity. This
process is relatively easy because the computer needs to compa
re two fingerprint
records
. The
verification process is referred as a ‘closed search’ because the search field
is limited. The second question is “who is this person?” This is the identification
function, which is used to prevent duplicate application or enrollment. In this case a
newly
supplied fingerprint is supplied to all others in the database. A match indicates
that the person has already enrolled/applied.


2.2

IDENTIFICATION


The identification process, also known as an ‘open search’, is much more
technically demanding. It involves ma
ny more comparisons and may require
differentiating among several database fingerprints that are similar to the objects.

Biometric Fingerprin
t Identification

Dept. of EEE


MESCE, Kuttippuram

3


3. BIOMETRIC SYSTEMS AND DEVICES


A biometric system is a combined hardware/software system for biometric
identification or verificat
ion
. Main functions of a biometric system are as follows:




Receive biometric samples from an enroller or candidate.



Extract biometric feature from the sample.



Compare the sample of the candidate with stored templates from
individuals.



Indicate identificati
on or verification upon the result of the previous
comparison.



Biometric devices have three primary components:



One is an automated mechanism that scans and captures a digital or analog
image of a living characteristic.



The second handles comparison of t
he image with the stored data.



The third interfaces with application systems.



These pieces may be configured to suit different situations. A common
issue is where the stored images reside; on a card presented by the person being verified
or at host comp
uter. Recognition occurs when an individual’s is matched with one of a
group of stored images.


Biometric Fingerprin
t Identification

Dept. of EEE


MESCE, Kuttippuram

4


4. BIOMETRIC ACCURACY






Biometric accuracy is the system’s ability of separating legitimate


matches from imposters. There are two important performance characteristics for
biometric systems.




False rejection is the situation when a biometric system is not able to verify
the legitimate claimed identity of an enrolled pers
on.



False acceptance is a situation when a biometric system wrongly verified the
identity by comparing biometric features from not identical individuals.



False Rejection Rate (FRR) refers to the statistical probability that the
biometric system is not able

to verify the legitimate claimed identity of an
enrolled person, or fails to identify an enrolled person.



False Acceptance Rate (FAR) refers to the statistical probability of false
Acceptance or incorrect verification. In the most common context, both
F
alse Rejection and False Acceptance represent a security hazard.

Biometric Fingerprin
t Identification

Dept. of EEE


MESCE, Kuttippuram

5


5. FINGERPRINT VERIFICATION


Fingerprinting is pr
obably the best
-
known biometric
-

method of identification
used for 100 years. Advances in computer technology and communication networks
hav
e made even huge fingerprint databases available for instant searches.



Among all the biometric techniques, fingerprint
-
based
Id
entification is the oldest
method that has been successfully used in numerous applications. Everyone is known to
have unique, i
mmutable fingerprints. A fingerprint is made of a series of ridges and
furrows on the surface of the finger. The uniqueness of a fingerprint can be determined
by the pattern of ridges and furrows as well as minutiae points. Minutiae points are local
ridge
characteristics that occur at either a ridge bifurcation or a ridge ending.



There are a variety of approaches to fingerprint verification. Some try to emulate
the traditional police method of matching minutiae, others are straight pattern matching
devic
es, and some adopt a unique approach all of their own, including thermal
properties and ultrasonic.

Finger
-
scan technology is the leading biometric authentication
technology in use today with the greatest variety of fingerprint devices presently
available.

This is partially due to the historical use of the fingerprint in law enforcement
as well as the fact that the technology lends itself to a more affordable solution.


VIEW OF A FINGER PRINT

Biometric Fingerprin
t Identification

Dept. of EEE


MESCE, Kuttippuram

6

6. FINGERSCAN


Fingerscan is an authentication terminal which ve
rifies a persons identity from
their finger image. When a user places their finger on the terminals scanner the image is
electronically read, analysed, and compared with a previously recorded image of the
same finger which has been stored in the fingerscan

database. Users call up their finger
image by keying in an identification number. This
ID

number does not need to be
classified as it is not part of the security system it simply retrieves the image that will be
compared to the users finger scan.



Finge
rscan contains its own database of finger images (called templates), user
privileges and authorities, and maintains a log of every transaction and message which
it records. The system can be accessed through a laptop, networked to a PC, or
connected via a
modem to a remote host computer.


6.1 THE TECHNOLOGY BEHIND FINGERSCAN


Fingerscan is a biometrics product which involves using some unique biological
characteristic or physical property of an individual to verify that persons claimed
identity. Biometrics
-
based identification replaces systems which rely on something a
person has in their possession, such as a key or
ID

card, or something a person knows,
such as a password or privileged information.

The imaging process is based on digital
holography, using
an electro
-
optical scanner about the size of a thumbprint. The scanner
reads three
-
dimensional data from the finger such as skin undulations, and ridges and
valleys, to create a unique pattern that is composed into a template file and recorded in
the finge
rscan database.


Biometric Fingerprin
t Identification

Dept. of EEE


MESCE, Kuttippuram

7


The pattern is not a fingerprint and a fingerprint cannot in any way be created
from the template. A template can only be compared with a newly presented live finger
image and not with other templates. One reason for this is that the dat
a capture process
used to create a template is random. If two templates were created one after another for
the same finger, each template would be different. This eliminates the possibility of
database matching and enhances users privacy.


6.2 THE ALGORIT
HMS


Fingerprint classification can be viewed as a coarse level matching of the
fingerprints. As input fingerprint is matched at a coarse level to one of the prespecified
types and then, at a finer level, it is compared to the subset of the database contai
ning
that type of fingerprints only.



An algorithm is developed to classify fingerprints into five classes, namely,
whorl, right loop, arch and tented arch. The algorithm separates the number of ridges
present in four directions (o degree, 45 degree, 90

degree and 135 degree) by filtering
the central part of a fingerprint with a bank of Gabor filters. This information is
quantized to generate a finger code which is used for classification. More recently, it
has become possible to scan a person’s finger
print into virtual storage in a computer
with the aid of laser technology. In order to prove identification, a person’s fingerprint
will be scanned again in the future by a similar device, and a match of print to name is
verified through information syste
m.




Biometric Fingerprin
t Identification

Dept. of EEE


MESCE, Kuttippuram

8

6.3 SYSTEM FUNCTIONS


The major
FINGERSCAN

functions are
:



Enrolment



Verification



Time Zones



Door access



Template management




Enrolment


Enrolment is the process of scanning a finger to create an image which is stored
as a template. Each time the us
er places his or her finger on the scanner the image is
compared to the one represented by the template to verify their identity.




A user with enrolment authority carries out enrolment at designated fingerscan
units. The process takes approximately 25 s
econds and the resultant template may be
stored in various places: in the unit itself, on a personal computer, in a mainframe
computer, on a smart card, and so on.




Each user enrolled is allocated a unique
ID

number, which they use to call up
their temp
late before scanning their finger. No
ID

number is required where the
template is stored on a smart card. Up to three fingers can be enrolled against the same
ID

number to provide users with more than one verification option. Ideally, one finger
on each ha
nd should be enrolled so that if the user injures the finger they usually use for
verification an alternate image is available.


Biometric Fingerprin
t Identification

Dept. of EEE


MESCE, Kuttippuram

9


This feature also provides for multi
-
person control, for example, if verification
from two users is required to open a safe.
In this situation fingerscan can be
programmed to require up to four fingers with different
ID

numbers to be verified
before access is granted.




Verification


Verification is carried out when a user either enters their
ID

number, or inserts
their smart c
ard in a smart card reader, and then immediately places their finger on the
reader platen. Verification takes about .5 of a second.



Verification for individual users can be set at various threshold levels to account
for users who may have very fine, wor
n, or damaged fingers. In this event reducing their
verification threshold can enhance the ease of use.



The overall system verification threshold can be lowered in situations where
little or no security is required, for example, time and attendance appl
ications. In this
situation it may be more acceptable to give a false acceptance than a false rejection.




Time zones


Up to thirty global or individual time zones can be defined in fingerscan. Each
user can have up to two active time zones at any time. Us
ers are allocated a default time
zone at enrolment, which can be changed by the system supervisor or from the host
computer.



Biometric Fingerprin
t Identification

Dept. of EEE


MESCE, Kuttippuram

10



Door Access


A door access list defines which users have access to the facilities controlled by
the fingerscan unit. The list ca
n be used in conjunction with time zones to restrict access
at certain times. The host computer system can control and manage the door access list
and the distribution of templates to each fingerscan unit.




Template Management


T
emplates can be stored in

the fingerscan unit, and/or a host computer, and/or a
smart card. Each fingerscan unit has 512Kbytes of non
-
volatile memory which stores up
to 300 templates. The memory can be expanded to 1.5Mbytes which will store more
than 1100 templates. Templates are
stored with a last used date status. If the memory
becomes full, the last used templates will be held locally in the fingerscan unit and the
main template database will be held in the host computer. The host will transmit
templates to individual units if t
he requested template is not found locally.



Templates can be deleted by user with Manager or Supervisor status either from
the host computer or locally at each fingerscan unit. Templates can be exchanged
between a fingerscan unit and the host computer o
ver fixed communications or modem
links, or locally to and from a laptop. A template created by the fingerscan unit can be
used on any other unit when loaded.


6.4


MANAGEMENT CONTROL

F
ingerscan

has four levels of management control:



User


A user submits a
finger for verification after entering an
ID

number

Biometric Fingerprin
t Identification

Dept. of EEE


MESCE, Kuttippuram

11



Enroller


An enroller has user status and can also enrol users onto the system.



Supervisor


A supervisor has enroller status and can also perform initial system set up
procedures, set time zones, set
alarm codes, and add and delete templates.



Manager


A manager has supervisor status and can also perform a total system reset, and
disable the supervisors ability to change the setup.



Transaction Log


A transaction log records every use of a
fingerscan

unit, the time it was used,
and the result. The log will hold at least the last 1000 transactions and will wrap around
when it becomes full. The transaction log cannot be erased except on a total system
reset by a user with Manager authority. Each transact
ion is allocated a consecutive audit
number that does not wrap around. The number will only be reset to 1 on a total system
reset.


6.5 SECURITY


Fingerscan provides an audit trail of the date and time a user accessed the unit,
the reason for access, and t
he result. With a 0.0001% probability of a false acceptance
fingerscan provides a level of security

which cannot be achieved by any

knowledge or
token based system
.




Template security


Before a user can do any action on a template such as enrol, delete, o
r transfer,
they must first have their identity verified by FINGERSCAN in the usual way. In doing
this, a record is added to the transaction log. Only users with Supervisor or Manager
authority levels can access the template database.

Biometric Fingerprin
t Identification

Dept. of EEE


MESCE, Kuttippuram

12




Software Security C
ontrol


A password option in the communications setup secures the data flow to a host
computer. When each fingerscan unit is initialised by the remote host, the host will
generate and download to the unit a unique Computer Generated Access Code
(CGAC)
of at least six digits. For all subsequent communications the host will check the CGAC
before starting the session and then change the CGAC immediately prior to logging off.

The CGAC can always be overridden by a Manager or Supervisor finger verifi
cation.
This is only likely to be required if the fingerscan unit is being accessed via a laptop PC.




Hardware security control


The processor board in the processor unit is located inside a metal box which
can be fitted with a tamper alarm if

required. The processor unit should always be
located inside the secure area in locations where
fingerscan

is providing access or other
security control.


Fingerscan

controls the activation of electric locks or strikes from the
processor board so the unit

cannot be hot
-
wired from outside.




Alarms Control



Send an alarm directly to a monitoring company, dialer, modem, siren, and so
on, and allow authenticated users to cancel and reset zone alarms and activate
and deactivate building services such as air co
nditioning and lighting.



Record alarms in the
fingerscan

transaction log.



Support a request to exit (REX) verification which allows users to open a door
from the inside. This can be used to monitor door forced alarms.



Door Lock Control


F
ingerscan

can
directly control a door lock strike after verification of a user.

Biometric Fingerprin
t Identification

Dept. of EEE


MESCE, Kuttippuram

13





Real Time Clock


Fingerscan
s real time clock is protected by a lithium battery, and features a day
-
of
-
week register and leap year correction.


6.6 AN OVERVIEW OF FINGERSCAN TECHNOLOGIES


The fundamental limiting factor for Finger
-
scan technology has been the process
by which the devices capture an image of the finger. The most common technologies
are: Optical, Silicon, Ultrasound and Touchless. Optical Scanner relies on an image of
rid
ges and valleys of the print. The process, referred to as Frustrated Total Internal
Reflection, a form of spectroscopy, essentially takes a picture of finger. Silicon or
Capacitance Fingerprint scanners often great potential because if utilizes higher i
mage
quality than optical surface contamination found on the finger. Thermal Fingerprint
scanners uses infrared to sense the temperature differences between the ridges and
valleys of the finger to create a fingerprint image. Ultrasonic Fingerprint scanne
r scans
the finger ultrasonically, using high frequency sound waves, to capture an image of the
finger.


6.7

CAPACITANCE SCANNER


Capacitive fingerprint scanners generate an image of the ridges and furrows that
make up a fingerprint. This type of scanner sense
s the print using electric current.

Biometric Fingerprin
t Identification

Dept. of EEE


MESCE, Kuttippuram

14



CAPACITANCE SCANNER



The diagram shown a simple capacitive s
ensor,
The sensor is made up of one or
more semiconductor chips containing an array of tiny cells. Each cell includes two
conductor plates, covered with a
n insulating layer. The cells are tiny


smaller than the
width of one ridge on a finger.




The sensor is connected to an integrator, an electric circuit built around an
inverting operation amplifier. The inverting amplifier is a complex semiconductor
device, made of a number of transistors, resistors and capacitors.



Like any amplifier


an inverting amplifier alters one current based on
flucturations in another current. Specifically, the inverting amplifier has the inverting
terminal and the non/inv
erting terminal. In this case the non
-
inverting terminal is
connected to ground, and the inverting terminal is connected to a reference voltage
supply and a feed back loop. The feed back loop, which is also connected to the
amplifier output, includes the

two conductor plates.

Biometric Fingerprin
t Identification

Dept. of EEE


MESCE, Kuttippuram

15

The two conductor plates form a basic capacitor, an electric component that
can store up charge. The surface of the finger acts as a third capacitor plate, separated
by the insulating layers in the cell structure and, in the case of

the fingerprint valleys, a
pocket of air. Varying the distance between the capacitor plates (by mainly the finger
closer or farther away from the conducting plates) changes the total capacitance (ability
to store charge) of the capacitor. Because of thi
s quality, the capacitor in a cell under a
ridge will have a greater capacitance than the capacitor in a cell under a valley.


To scan the finger, the processor first closes the reset switch for each cell,
which shorts each amplifier input and output to ba
lance the integrator circuit. When the
switch is opened again, and the processor applies a fixed charge to the integrator circuit,
the capacitors charge up. The capacitance of the feedback loop’s capacitor affects the
voltage at the amplifier’s input, wh
ich affects the amplifier’s output. Since the distance
to the finger alters capacitance, a finger ridge will result in a different voltage output
than a finger valley.


The scanner processor reads this voltage output and determines whether it is
character
istic of a ridge or an valley. By reading very cell in the sensor array, the
processor can put together an overall picture of the fingerprint, similar to the image
captured by an optical scanner.


The main advantage of a capacitive scanner is that it requ
ires a real fingerprint


type shape rather than the pattern of light and dark that make up the visual impression
of a fingerprint. This makes the system harder to trick. Additionally since they use a
semiconductor chip rather than a CCD (charge coupled
device) unit as in case of Optical
scanner, capacitive scanners tend to be more compact than Optical devices.

Biometric Fingerprin
t Identification

Dept. of EEE


MESCE, Kuttippuram

16


6.8

ADVANTAGES OF FINGERPRINT SCANNERS

Compared to the other biometric authentication technologies, fingerprint
scanners are:



The most widely availab
le device.



Relatively low cost



Small size (easily integrated into keyboards) and



Easy
to integrate



Fingerprint verification may be a good choice for in
-
house systems where
adequate explanation and training can be provided to users and where the system i
s
operated within a controlled environment.


6.9

DISADVANTAGES


Fingerprint verification can suffer under large
-
scale usage. In a large
population, poorly trained users cause higher usage errors and hence higher instances of
false rejection. Also, the user i
nterface (scanning module) can become damaged or
dirty by large
-
scale usage.

Biometric Fingerprin
t Identification

Dept. of EEE


MESCE, Kuttippuram

17


7.

FUTURE APPLICATIONS

There are many concerning potential fingerprint applications, some popular
examples being:


7.1

ATM MACHINE USE

Most of the leading banks have been experimentin
g with biometrics of ATM
Machines use and as general means of combining card fraud. It is estimated that lesser
due to identity fraud in welfare disbursements, credit card transactions, cellular
telephone calls, and ATM withdrawals total over $ 6 billion
every year. At present an
ATM identifier a person as a client after the person inserts an ATM card into the
machine and enters a personal identification number (PIN). This method of
identification has its drawbacks. According to researchers, about one
-
f
ourth of bank
customers apparently write their PIN on their ATM card, thus defeating the protection
offered by a PIN when an ATM card is stolen.


7.2

INTERNET TRANSACTIONS

Security for information systems and computer networks is another important
area for fin
gerprint applications. Access to databases by means of remote login is
another application. Some experts anticipate that more and more information systems,
computer networks, and world wide web sites will use fingerprint identification
techniques to cont
rol access and for other security purposes.




Biometric Fingerprin
t Identification

Dept. of EEE


MESCE, Kuttippuram

18

7.3

PERSONAL TRANSPORTATION


Several leading automobile manufacturers are exploring the use for fingerprint
identification to enable an authorized driver to enter and start a car without using a key.


7.4

USE IN PUBLI
C SECTOR


Various government agencies have considered using biometric fingerprint
identification. In benefits distribution programs such as welfare disbursement,
fingerprint identification techniques could bring about substantial savings by deterring
the
same person from filing multiple claims. Fingerprint based voter registration can be
used to verify identity at the polls to prevent fraudulent voting.

In
Academics/certifications it can be used to verify person’s identity prior to taking an
exam.

Biometric Fingerprin
t Identification

Dept. of EEE


MESCE, Kuttippuram

19


8.

CONCL
USION


Biometric fingerprint identification has many usability advantages over
traditional systems such as passwords. Specifically, users can never lose their
fingerprints, and the fingerprint is difficult to steal or forge. The intrinsic bit strength of

a fingerprint is quite good when compared to conventional passwords. Finger scanners
are getting smaller, cheaper, and more accurate, and can be used in mobile gadgets
without sprucing up the size, cost, and power consumption. By using this technology
t
heft can be prevented and can also eliminate fraudulent transactions. Mobile
manufacturers and wireless operators are incorporating voice and fingerprint scanning
techniques in their devices. Fingerprint is a very strong desktop solution, and it is
antic
ipated that the desktop will become a device for biometric revenue derived from
product sales and transactional authentication. Most middleware solutions leverage a
variety of fingerprint solutions for desktop authentication.



Fingerprint is a proven tec
hnology capable of high levels of accuracy. Strong
fingerprint solutions are capable of processing thousands of users without allowing a
false match, and can verify nearly 100% of users with one or two placements of a
finger. Because of this, many finger
print technologies can be deployed in application
where either security or convenience is the primary driver. Reduced size and power
requirements, along with fingerprint’s resistance to environmental changes such as
background light and temperature, allow

the technology to be deployed in a range of
logical and physical access environments. Fingerprint acquisition devices have grown
quite small sensors slightly thicker than a coin, and smaller than 1.5 cm x 1.5 cm, are
capable of acquiring and processing i
mages. Thus fingerprint has emerged as a highly
distinctive identifier, and classification, analysis and study of fingerprints has existed
for decades.


Biometric Fingerprin
t Identification

Dept. of EEE


MESCE, Kuttippuram

20



9.
REFERENCES

1.

Electronics for you


June 2002

2.

RSA Secu
rity’s official guide to CRY
PTOG
RAPHY BY Steve Burnett and
Stephen Paine.

3.

Infokairali


December 2001.

4.

http://www. biometricgroup.com.

5.

Encarta Encyclopedia 2002.

6.

http://www. howstuffworks.com.

7.

http: /
/
www. BiometricID.org.


















Biometric Fingerprin
t Identification

Dept. of EEE


MESCE, Kuttippuram

21


ABSTRACT



Identification of individuals is a very basic societal requirement. Electronic
verification of a person’s identity is of great importance as more interactions take
place electronically. Biometric fingerprint identification

is a technique used to
change the physical attribute of a person ie; his finger print into electronic
processes. Until recently electronic verification was based on something the
person had in their possession like a passw
ord. But the problem is that these
forms aren’t very secure because passwords can be forgotten or taken away. In
biometric finger print identification a scanner is used to get the image of the
finger. When a user places h
is or her finger on the terminals of scanner the
image is electronically read, analysed and compared with a previously recorded
image of the same finger, which has been stored in finger scan data base.
Finger print is a

proven technology capable of high levels of accuracy.

Biometric Fingerprin
t Identification

Dept. of EEE


MESCE, Kuttippuram

22


ACKNOWLEDGEMENT




I express my sincere gratitude to
Dr.Nambissan,

Prof. & Head,
Department of
Electrical and Electronics Engineering, MES College of
Engineering, Kuttippuram, for his cooperat
ion and encouragement.


I would also like to thank my seminar guide
Mrs.
Renuka.T.K
.

(
Lecturer, Department of EEE
)
,
Asst. Prof. Gylson Thomas.

(Staff in
-
charge,
Department of EEE) for their

invaluable advice and wholehearted cooperation
without which this

seminar would

not have seen the light of day.


Gracious gratitude to all the faculty of the department of EEE &
friends for their valuable advice and encouragement.














Biometric Fingerprin
t Identification

Dept. of EEE


MESCE, Kuttippuram

23


CONTENT
S


1. INTRODUCTION






1

2. IDENTIFICATION AND VERIFICATION SYSTEMS

2

3. BIOMETRIC SYSTEMS AND DEVICES



3

4. BIOMETRIC ACCURACY





4

5. FINGERPRINT VERIFICATION




5

6. FINGERSCAN







6

6.1 THE TECHNOLOGY BEHIND FINGERSCAN


6

6.2 THE ALGORITHMS






7

6.3 SYSTEM FUNCTIONS





8

6.4 MANAGEMENT CONTROL




10

6.5 SECURI
TY







11

6.6 AN OVERVIEW OF FINGERSCAN TECHNOLOGIES

13

6.7 CAPACITANCE SCANNER





13

6.8 ADVANTAGES OF FINGERPRINT SCANNERS


16

6.9 DISADVANTAGES






16


7. FUTURE APPLICATIONS





17

8.
CONCLUSION







19

9.
REFERENCES







20