Last week
we took a philosophical look at encouragement, the "little things" and level 3 detail.

This week
Jennifer Hannaford shares an example of a friction ridge recording that we should all be aware of.
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Anomalies of Livescan Capture

“The goal that is to be addressed in any situation is to obtain a recording of the friction ridge skin that is of adequate quality for the comparisons that are subsequently to be made.  Ideally, such prints will have good contrast, clear detail, and be complete.” - Cowger

The history of exemplar capture for latent prints has mainly stressed the three main points listed above:

• Contrast
• Clarity
• Completeness

 Perhaps, there is another criterion to consider; accuracy.

With the ever growing and popular use of digital technology, the acquisition of exemplar prints using livescan should be explored and understood by latent print examiners.  How accurately does this technology convey the spatial relationship of details within the friction ridge skin?  How accurately does this technology depict the existing minutiae in the represented friction ridge?

Individuals within the fingerprint community need no reminder of the principles upon which the individualization through the use of fingerprints is based.  Yet, a statement of these points will emphasize the importance of the information upon which we rely when using any standard for a comparison: 
 

§         Friction ridges are permanent.  Friction ridges are permanently formed during fetal development and remain the same, barring scarring or amputation, until death and decomposition sets in.

§         Friction ridge formations are unique.  No two areas of friction ridge skin are the same on two different people, identical twins or on two areas of friction ridge surfaces upon the same person.

§         If there are areas of dissimilarity that cannot be explained, the origin is not the same.
 

Thus, upon any capture of the friction ridge information, whether it be a latent or an exemplar, the impression will demonstrate the uniqueness of that friction ridge skin in the manner that it exists.

Throughout my experience as a latent print examiner I have conducted many comparisons.  I have used exemplars/standards that have varied in their methods of capture.  They have included traditional printer’s ink, modern ink methods, photocopies of these varieties and livescan images.  Recently, a routine comparison using a set of livescan exemplars caught my attention.

Did these prints originate from the same area of friction ridge skin?



What about the one-dissimilarity doctrine?

“A doctrine has emerged in fingerprint comparison...if two fingerprints differ in a single ridge characteristic the prints cannot be attributed to the same finger or individual.”-Thornton

In fact, these two examples originated from the same area of friction ridge skin, both images reside on the same card, and they were captured during a single exemplar recovery event.

The example on the left is the rolled image of the right middle finger.  The image on the right is the right middle finger captured as the flat.  During comparison of a latent of limited detail to the rolled impression in the above example, I concluded that the whorl I was examining could not have originated from this individual.  The conclusion was based on a single bifurcation present at the core of the latent to the double bifurcation arrangement in the corresponding area at the core in the exemplar.  Upon closer inspection of the exemplar set, it was determined that this individual could not be eliminated.  The information between the flat and the rolled impression, although originating from the same area of friction ridge skin, did not agree.

After this experience, I have taken a closer look at the livescan images I use for comparisons and have noticed similar anomalies.  In addition to inaccurate capture of detail, I have observed what appears to be a distortion of the spatial relationship of minutiae.

To this point, I have only observed artifact and distortion within the rolled exemplar images.  So, what is the mechanism behind the occurrence?  I am not an expert in digital technology, nor do I have any experience operating a livescan system.  However, by personal observation, I offer a possibility as an explanation.  There appears to be a double or repeated capture of friction ridge skin in the final image.  This may occur from slippage, hesitation or changes in pressure of the finger being rolled on the platen surface during capture, obscuring the information.  Although the area recaptured is very small, the additional information may blend with the rest of the print, causing extra detail to appear natural within the impression.  One has to wonder if this is an operator issue, an instrument issue or a combination of both.  Regardless of the mechanism, the fact remains that this phenomenon has been documented, and the presence of artifact may be subtle enough to go undetected (especially if it is a condition the viewer is not actively looking for).

The intention of this communication is to share with the fingerprint community the possibilities that one might encounter when using livescan images.  Each examiner should strive to understand what is being examined and be prepared to explain this type of distortion if it needs to be addressed in court.

What other effects might an artifact in a livescan image have on the comparison process?  Could an artifact in the exemplar lead to an erroneous elimination?  The example given above supports the possibility when one is provided with limited information in a partial latent print.  But, could the converse be true?  Could an erroneous identification occur?  No.  Just as uniqueness of friction skin is established through the random biological development of ridge detail, a random arrangement achieved digitally can not recreate the uniqueness of any another area of friction ridge skin.

Examiners may ask themselves if this medium is reliable if the possibility of artifact exists.  It is reliable, with the caveat that one must be aware of the possibility of the existence of anomalies.  Moreover, correspondence of detail within an image can be determined and confirmed through comparison of the rolled and flat impressions.

I hope to continue exploring this topic and encourage those who find unusual conditions, found in any capture medium, to share them with the Latent Print Examiners at the Vermont Forensic Laboratory.  I can be reached directly by email at jhannafo@dps.state.vt.us

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To discuss this Detail, the message board is always open: (http://www.clpex.com/phpBB/viewforum.php?f=2)

More formal latent print discussions are available at onin.com: (http://www.onin.com)

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