How biometrics works to help you get through airport security in a hurry

Question: I recently had surgery on my hand and am quite certain that the handprint will no longer match that on the Global Entry database. I have two international trips coming up and I’d really like my Global Entry to be up to date. What should I do?

Don Brown

Long Beach

Answer: Brown doesn’t have to do anything to use his Global Entry privileges, which include expedited re-entry into the United States and screening at domestic airport security, all for $100 for five years.

Customs and Border Protection, which administers Global Entry, said it is fingerprints, not handprints, that are used for identification. The re-entry kiosks at immigration, a spokesman said, use four fingerprints from one hand to validate who you are.

If something were amiss at re-entry, the spokesman said, the traveler would get expedited screening from a Customs officer.

But what could go wrong with fingerprints?

Ask a criminal. Or a bricklayer. Or a nurse. Or an older person. Or someone taking certain medications.

Any one of those categories may create problems with this form of biometric identification.

Biometrics? Isn’t that a new thing? How can prints be biometric?

The word “biometrics” seems to conjure all sorts of futuristic notions about how we will be identified, but the truth is that fingerprints, which are classified as biometrics, have been used as identification in criminal work since about 1900, according to “Biometrics for Dummies,” by Peter Gregory and Michael Simon, “dummy” being the category I fell into by thinking I knew more about biometrics than I actually do.

In fact, when I considered the issue, which has implications and applications for travel, I realized I didn’t really know what biometrics is.

But James Wayman, a senior fellow in the Office of Research at San Jose State University, does. “Biometric technologies recognize persons (human bodies) automatically based on biological and behavioral traits,” he said in an email “These technologies include fingerprint, iris, face and hand shape recognition, all of which are being currently used in travel systems around the world.”

(Biological traits, “Dummies” said, include your signature, voice, gait and keystroke. Typing? Yes. “The rhythm of someone’s typing [or keyboarding as we tend to call it these days] is as unique as someone’s signature,” it said. Who knew I was betraying myself even as I write this?)

But it’s my fingerprints, not the way I type, that are on file with Global Entry, and it’s the fingerprints that many criminals worry will betray them.

“Fingerprints can be both intentionally and accidentally scarred to avoid recognition,” Wayman said. “It is said that John Dillinger, the famous U.S. criminal, intentionally scarred his fingerprints.”

No wonder. As anyone who has watched a police procedural knows, fingerprints are unique. Or are they? In his memoir, “Written in Blood,” author and forensic scientist Mike Silverman wrote, “Although everyone’s fingerprints are, theoretically, unique, there are prints which can be very similar and this can occasionally cause difficulties.”

He noted that a suspect in the Madrid train bombing of 2004 was wrongly (sorry) fingered. “Despite the way fingerprint evidence is portrayed in the media, all comparisons ultimately involve some human element and, as a result, they are vulnerable to human error,” Silverman wrote. The wrongly accused man received a $2-million settlement.

One more problem, Wayman noted: “Fingerprints are easily damaged.” Bricklayers handling rough material can sometimes wear down their prints, according to a 2009 article in Scientific American. Nurses’ prints may be less distinct, it’s thought, because of repeated hand washing. “Older people are harder to recognize through fingerprints than younger people,” Wayman said, “but that seems to be caused by biological changes to the skin rather than injury.” And certain kinds of medication, including a kind of chemotherapy that can induce hand-foot syndrome, may create havoc with prints.

The good news is that people who want to get through security faster won’t be denied just because they may have problems with their prints, Customs said.

Wayman has been working with the SmartGate program, an Australian system that relies on mathematically based facial recognition, he said in a phone interview. It measures distances between certain facial features and compares your passport picture. Weight loss or a face-lift won’t interfere with the computations.

That may, indeed, be the wave of the future. Some of these more futuristic technologies may seem a bit invasive until you consider that 5.6 million sets of fingerprints were stolen from U.S. federal employees last year in a hack attack. Unlike a password, a fingerprint isn’t quite as easily changed.

One day, the distance between our facial features or the structure of our irises may be our keys to returning to the U.S. For now, fingerprints get the thumbs up for the nearly 3 million people who have Global Entry.

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