Transcript 80654_fingerprints

Fingerprints
History
• Replaced anthropometry during early
20th century
• 1903: William West incident
– Fort Leavenworth prison
– Urban legend: prisoner William West
couldn’t be distinguised from inmate with
same name by anthropometry
Fundamental Principles of
Fingerprints
1. No Two Individual will have identical
fingerprints
2. Fingerprints stay the same throughout
our lives
•
Attempts at destroying pattern has failed
3. Limited variety in patterns allows
systematic classification of an
individuals fingerprints
Three Ways to Leave a
Fingerprint
1. Invisible (latent) print
•
Leave the sweat and oils on a surface
2. Visible print
•
Touch a colored liquid, then leave it on a surface
3. Plastic print
– Touch a soft surface that will mold to your ridge
characteristics
Latent Prints
• Made up of
– Oils, picked up from areas that contain hair
– Amino acids, also from areas that contain
hair
– Salt, from sweat
– H2O, from sweat
Fingerprint Patterns
• Loops
– Ridge lines enter from one side and curve around
to exit from the same side
– 60-65% of population
• Whorls
– Rounded or circular ridge pattern
– 30-35% of population
• Arches
– Ridge lines enter from one side of print and exit
out the other
– 5% of population
Features Used in Classification
Other Ridge Characteristics
•
•
•
•
•
•
Enclosure/lake
Bifurcation
Short ridge
Ridge ending
Ridge crossing
Island
6 Ridge Characteristics
• Bifurcation- one ridge splits into two
• Enclosure- ridge splits then comes back
together
• Ridge ending- ridge stops
• Island or Dot – ridge that looks like the dot on
an i
• Ridge crossing- two ridges cross one another
• Short Ridge- ridge that is longer than an
island but not very long
Ridge Characteristics
• Bifurcation
• Ridge Ending
Ridge Characteristics
• Island/Short Ridge
• Enclosure
Loops
• Radial loops open towards thumb
• Ulnar loops open toward pinky
• Have one delta
• must have one
or more ridges
entering and exiting
from the same side
it began
Loop Example
• Which type of loop
is this if located on
the left hand?
Whorls
Plain
• Two deltas
• A plain or central pocket
whorl have at least one
ridge that makes a complete
circuit
Double Loop
Central pocket
Arches
• No deltas
Example #1
Example #2
Example #3
Classification system
• Henry used system of assigning values
to particular pattern types on each of
ten fingers
• Called primary classification
• 25% are 1/1
• Less useful since digital imaging
Henry Numbering system
L
Pinky
L
L
Ring middle
L
L
Index Thumb
R
Thumb
R
Index
R
Middle
R
Ring
R
Pinky
Finger 10
#
9
8
7
6
1
2
3
4
5
Value
if
whorl
1
2
2
4
16
16
8
4
4
1
Henry # = 1+ (sum of even finger #s)
1+ (sum of odd finger #s)
don’t reduce the fraction!
AFIS
• Automated Fingerprint Identification
system
• Digitally encodes fingerprints by ridge
ending and bifurcations
• Allows high-speed computer
comparison
• Software can subtract out background
or enhance image