(CNN) — Orlando’s airport is the first in the nation to expand automated facial recognition technology to all international travelers, which means about 5.9 million faces a year will go on record with the US government.

Orlando International Airport, the busiest in Florida, has been testing the system with flights mostly to and from London’s Gatwick Airport, airport spokesman Rod Johnson said. Airports in Atlanta, New York and Miami and other cities are in the testing phase now. Orlando’s system is expected to be fully operational by the end of this year, Johnson said.

US Customs and Border Protection said the technology is 99% accurate and helps to thwart terrorism. Airport officials said it cuts plane loading time by eliminating the need to present a boarding pass.

The American Civil Liberties Union objects to the facial recognition data collection and use, saying it’s not reliable across gender and race and can be misused to monitor citizens’ activities beyond the airport.

Customs and Border Protection said it is confident the biometric system will heighten security without infringing on anyone’s privacy.

The “CBP has a comprehensive name-based system (biographic) that vets and checks foreign nations entering and departing the United States. A name-based system, by itself, cannot verify the identity of persons presenting travel and identity documents,” agency spokeswoman Jennifer Gabris said in an email.

“The best tool to combat this fraud is to biometrically verify that a person who presents a travel document is the true bearer of that document.”

Statistics for how many potentially suspect travelers have been flagged with the face-scanning tool are not available, she said.

Biometric images — human features stored as data – are being temporarily stored for 14 days while Customs and Border Protection continues to assess the effectiveness of the Orlando program and other airport pilot programs, said John Wagner, the agency’s deputy executive assistant commissioner for the office of field operations. Eventually there will be no need to store the photos. No new privacy concerns are at stake as the federal government already holds millions of Americans’ passports, he said.

But the ACLU remains skeptical.

“There’s a real lack of clarity about how the data is stored and used,” said Neema Singh Guliani, senior legislative counsel for the ACLU. Should the images from the boarding gates be stored, they can be used “surreptitiously by the government and private actors to track people without their knowledge,” such as identifying people at a protest, she said.

How it works to depart the United States:

• Customs and Border Protection creates a biometric sketch of passenger pictures and stores them in a private virtual cloud.
• A traveler comes to the departure gate — a set of clear saloon-like doors — and stands for a photo that is matched — or not — with what is in the database.
• If there is a mismatch, a passenger can supply his or her passport or visa.

How it works to re-enter the United States:

• Customs and Border Protection collects photos from existing government databases, such as visa and passport pictures, based on the flight manifest and builds a gallery.
• Passengers step up to the inspection booth for another photograph for matching with the database.
• Interviews and luggage inspections are still part of the customs process.

Congress in 2004 mandated collection of biometric information for noncitizens leaving and entering the country. US citizens can opt out. Instead, they can show their passports and boarding passes.

“They have to show they are who they say they are,” the Orlando airport’s Johnson said.

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