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 –H 2 O, 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 BifurcationRidge Ending

Ridge Characteristics Island/Short RidgeEnclosure

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 Two deltas A plain or central pocket whorl have at least one ridge that makes a complete circuit Plain 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 Ring L middle L Index L Thumb R Thumb R Index R Middle R Ring R Pinky Finger # Value if whorl 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