SciTech Calculating The Rarity Of A Fingerprint


1947-2014 (Archived)
Jun 17, 2004
Although fingerprints are unique to every individual, crime scene prints are usually incomplete patterns taken off doorknobs or glass.

Knowing the rarity of a partial print could be useful to forensic scientists who are trying to determine how valuable a fingerprint is as evidence, said Sargur Srihari, a computer scientist at the University at Buffalo who is leading the research.

Rarity is already used as an evaluation tool.

“Consider the simple case where an offense was committed by someone who is seven feet tall,” said Dr. Srihari. “That is a pretty rare height, so it’s valuable evidence in helping to identify the person.”

Another example is DNA. Forensic analysts can determine how rare a particular DNA pattern is and then choose to use this to identify possible culprits.

Dr. Srihari and his graduate student Chang Su say they have done the same for fingerprints.

“It’s purely mathematical,” Dr. Srihari said. “We’re simply saying, ‘We just found something that is unusual, and that makes it an important piece of evidence.’ ”

To do the research, the scientists defined fingerprints as a series of points, composed of the endings of ridges and ridge bifurcations.

They then pulled from a database of 4,000 fingerprints kept on file at the National Institute of Standards and Technology and created a computer system that can read fingerprint patterns. Based on a print’s points, the system can mathematically determine its rarity.

Today, forensic scientists make this call without the aid of technology.

“They might find hundreds of prints at a crime scene, and right now the analysis is done intuitively by human examiners,” Dr. Srihari said. “But we can calculate that.”

The research was presented this week in Vancouver, British Columbia, at the annual Neural Information Processing Systems conference.

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