THE SCIENCE OF

FINGERPRINT

IDENTIFICATION

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Friction Ridge Identification is generally understood to be the individualization of the ridge detail found on the end joints of the fingers, since those areas are taken for record and/or filing purposes. The technique of identifying fingerprints is

equally applicable to identifying any of the other ridged areas of the hand or foot

Module # 6

Visual Component of Identification

When a human looks at a number, letter or other shape, neurons in various areas of the

brain’s visual center respond to different components of that shape, almost instantaneously

fitting them together like a puzzle to create an image that the individual then “sees” and

understands. The eye lens, is perfectly clear, perfectly curved and is capable of focusing on an

incredible amount of data. But vision is only partly to do with the retina, lens, and cornea.

Understanding what we see, happens in the brain, which is why a person with perfect vision is

still susceptible to optical illusion. Our visual nervous system approximates color, shape, and

dimension. The process of seeing begins with the presence of light, an image formed on the

retina, and an impulse transmitted to the brain, but there are many other factors that play a

part in how we perceive visually. Our perceptions are influenced by our past experiences,

imagination, and associations. In a tenth of a second, we can recognize something we see as

an animal or not. Studies show this immediate, rough impression probably depends on

recognizing just one or more individual parts of what we see. Fine discriminations – such as

recognizing individual faces – take longer to happen, and the studies suggests that this delay

depends upon emerging signals for combinations of shape fragments. The brain has to

construct an internal representation of an object from disparate pieces.”

Let’s have a little FunIn the image to the right you could interpret it as a portrait

of an older man, but when you look closer you’ll see a

number of faces, images and silhouettes of faces. Why does

our mind interpret the images we see in this way?

The simple explanation is our mind assimilates the image

we see and compares it with information already stored in

our brain. In a recent Cambridge University study it was

found that as long as the 1st. and last letters in a word were

correct it didn’t matter if the other letters were mixed, a

person could still read the paragraph or sentence correctly

interpreting what the writer meant. An example of how our

perceptions are influenced by our past experiences,

imagination, and associations which can create a

dilemma when doing fingerprint comparisons. It is critical

you are objective when doing your analysis and evaluation

of ridge detail, you cannot expect to see something based

on past knowledge/experience. You have to work at being

completely objective. The best way to accomplish an

unbiased comparison is by following the analysis,

comparison, evaluation and validation procedure.

Objective Analysis

When doing a fingerprint comparison your going to be asked to make an objective

decision based on what you see in front of you and not be influenced by subjective

reasoning. The brain will attempt to assist you in recognizing images, it could give you a

perception of something that is not there.

How many of us read A Bird in the Bush, not noticing THE is repeated

Fingerprint Examiners are allowed to make positive

identifications with:

There is not a required minimum number of minutiae required for an experienced examiner to

individualize a fingerprint comparison. Individual agencies may have policies and procedures

on what they feel constitutes an individualization. In this training course I will require 12 points

for identification, similar to Locard theory on identification. Requiring a set number of minutiae

is a training aid, to insure the student understands the value of minutiae along with gaining

experience in minutiae analysis/comparison. The individuals taking this course may have no

or limited experience in the individualization of friction ridge detail. The average fingerprint

contains between 75 and 150 points of identification and since we will be dealing with mostly

very good images, a 12 point minimum will work well. I would encourage students during the

training to exceed the minimum the course requires.

Appropriate Training

Appropriate Experience

Appropriate Ability

Following agency policy.

The Verification Process

The process of making a fingerprint comparison

between a search fingerprint image and the

suspect fingerprint image. Whether you are

doing a comparison of one (1) image or

multiple fingers the process is always the same:

Analysis

Comparison

Evaluation

In latent fingerprint comparisons and most

state ten print systems there is also a:

Validation process

Analysis

Comparison

Evaluation

Validation

Referred to as the Scientific Method

of fingerprint individualization.

Analysis – the qualitative and quantitative assessment of Level 1, 2, and 3 detail to determine their proportion, interrelationship and value to individualize.

Comparison – to examine the attributes observed during analysis in order to determine agreement or discrepancies between two friction ridge impressions.

Evaluation – the cyclical procedure of comparison between two friction ridge impressions to effect a decision, i.e., made by the same friction skin, not made by the same friction skin, or insufficient detail to form a conclusive decision.

Validation - It is highly recommended that all fingerprint identifications be validated by 2nd. examiner or electronically in an AFIS.

Note:

Many state agencies do not require a 2nd. verification on ten print identifications of

arrest/applicant cards. Larger states and the FBI do require a validation ( 2nd. Verification).

A second verification may be done by a qualified fingerprint examiner or possibly electronically,

using lights out technology. The single verification makes a system vulnerable to

identification errors.

EVALUATION

Search Image Suspect Image

Area’s of concern when comparing possible identifications

#1As every examiner knows, search and exemplar (database) images are never exactly the same. The

reasons are many; how the exemplar was recorded or temporary or permanent damage to the fingers,

etc. The fingerprint examiner during the analysis and evaluation must be able to understand and

explain any discrepant points found in either the search or exemplar images. The 1 discrepancy rule ,

if there is 1 unexplainable discrepancy in either the search or exemplar image an individualization

cannot be made. These images are from the same card the rolled and plain impression of the right

thumb.

Area’s of concern when comparing identifications

#2

The 2nd. major area of concern is suspect images produced in today’s automated

fingerprint systems often have very similar constellations of points of similarity. Despite

the unusual similarity in the relationship between points in many prints, the prints may not

be identical fingerprints. The enormous size of today’s AFIS databases and the power of

the search algorithms can find a confusingly similar print to the one being searched. As

databases increase and algorithms improve, there will be more suspects produced, that

will have unusual similarity between points but will not be the individuals print. So can

this type of error be prevented ? The answer is “yes” we can minimize the numbers of

these type errors with good training and adherence to procedure.

Area’s of concern when comparing possible identifications

#3

The 3rd. Area of concern is when an examiner uses "backward " reasoning. In effect

allowing yourself to be influenced by the search print in effect by working backward from

the suspect print. The examiners will find features in the print being searched and then

look for them in the image being searched. The danger is in poor quality images murky or

ambiguous points may be erroneously identified. When an examiner is dealing with a

poor quality latent that lacks clarity, it is tempting to look at the exemplar and work

backward but it can have disastrous results.

Area’s of concern when comparing identifications

#4

To much reliance on Level III detail. Level III detail can include a number of things from

ridge shape and pores to scars and this information can be beneficial in individualization

when properly used. In ten print searches this should not be a big issue because the

clarity and amount of minutiae available is significant. While level III detail can be helpful,

it becomes less helpful as clarity decreases. I have seen cases where the ten print image

or suspect images are so poor that you in effect are making a comparison very similar to

a latent comparison and Level III detail may be required to effect an identification.

Area’s of concern when comparing identifications

#5

In an AFIS search the examiner is given two (2) search and two (2) target images. While

the examiner may be tempted to identify based on level 1 similarity between these four

(4) images, this could result in an erroneous identification. The examiner must utilize the

analysis, comparison and evaluation steps.

DISTORTION CAUSED BY SCAR

1st. glance the images look dissimilar but look in the delta area.