Fingerprints

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Fingerprints
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History

• Replaced anthropometry during early 20th century
• 1903 William West incident
• Fort Leavenworth prison
• Urban legend prisoner William West couldnt be
  distinguised from inmate with same name by
  anthropometry

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Fundamental Principles of Fingerprints

• No Two Individual will have identical
  fingerprints
• Fingerprints stay the same throughout our lives
• Attempts at destroying pattern has failed
• Limited variety in patterns allows systematic
  classification of an individuals fingerprints

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Three Ways to Leave a Fingerprint

• Invisible (latent) print
• Leave the sweat and oils on a surface
• Visible print
• Touch a colored liquid, then leave it on a
  surface
• Plastic print
• Touch a soft surface that will mold to your ridge
  characteristics

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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

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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

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Features Used in Classification
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Other Ridge Characteristics

• Enclosure/lake
• Bifurcation
• Short ridge
• Ridge ending
• Ridge crossing
• Island

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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

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Ridge Characteristics

• Bifurcation

• Ridge Ending

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Ridge Characteristics

• Island/Short Ridge

• Enclosure

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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

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Loop Example

• Which type of loop is this if located on the left
  hand?

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Whorls

• Two deltas
• A plain or central pocket whorl have at least one
  ridge that makes a complete circuit

Plain
Double Loop Central pocket
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Arches

• No deltas

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Example 1
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Example 2
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Example 3
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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

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Henry Numbering system
L Pinky L Ring L middle L Index L 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 1 2 2 4 16 16 8 4 4
Henry 1 (sum of even finger s) 1
(sum of odd finger s) dont reduce the
fraction!
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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

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