A growing number of airports across the U.S. are using facial recognition scanners.

Philadelphia International Airport (PHL) is the latest to roll out the technology. “So, this is an electronic way, basically, to verify identity,” said Jeni Best, a branch manager with U.S. Customs and Border Protection (CBP).

At PHL, the machines are set up at three international gates. Passengers will step up to the machines and have their faces scanned before boarding their flight. CBP officials say it takes less than two seconds and has a 99 percent matching rate.

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“It reduces your imposter threat, and it provides a secure and efficient way to verify identity,” Best said.

According to Best, the ultimate goal is for the machines to eliminate the need to show passports. But some people fear the technology threatens their privacy.

“It’s really a very big deal," said Paul Hudson, president of the nonprofit Flyers Rights. Hudson has been working for the airline passenger advocacy group for more than 20 years. His concern is where the photos from the machines end up. "The databases are, first of all, are not immune to hacking,” he said.

CBP officials say all photos of U.S. citizens are deleted within 12 hours. Photos of non-U.S. citizens can be stored on CBP systems for up to 75 years. "But that is a practice that CBP already has in place for all visitors," Best added.

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“I’d have to think about it for a little bit,” passenger Ellyn Phair said. “There are so many things going on with hacks on the computer systems and that is increasing these days, so I feel like that could be a problem.”

Hudson thinks more research needs to be done. “Before you do something like this, there needs to be a buy-in by a large majority of the population,” he said.

At least 27 airports in 16 states and D.C. are using facial recognition technology. In Philadelphia, the machines are part of a pilot program, so passengers have the ability to opt out of using them. “They just let, either let the gate agent know or the CBP officer," said Best.

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Some argue opting out isn't as easy as it seems. “Based on research I’ve seen, only two percent actually opt out, so that would indicate that people either don’t understand it or [...] it’s too bothersome to deal with,” Hudson said.

“Right now, it’s an experiment,” said Angelo Reid, who has been working at PHL for more than 40 years. In fact, he’s retiring this week.

“I don’t where the years went but they’re gone,” Reid said. Throughout the years, he says he’s seen a lot of changes. “It grew as we went along. And so did security,” he explained.

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Reid thinks face scanners are just another way to keep people safe. “Just like anything else, people will grow into it. They’ll get used to it. And they’ll realize it’s for their own safety,” he added.

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At PHL, the face scanners are running as a pilot program for 45 days. Once the program ends in early March, the airport will likely decide whether to implement them long-term.