Denver International Airport travelers flying to other countries this week faced new facial recognition scanners at 15 gates, the latest technology deployed to boost security under a mandate from Congress.

This new U.S. Customs and Border Protection system compares a traveler’s photo to images already kept by the government, including passport and visa photos. The Transportation Security Administration agents at airport security checkpoints already use facial recognition technology when screening all travelers.

DIA officials announced in a news release this week that the facial scanning process takes about 3 seconds. They cast this as faster, better for the flow of travelers at the airport, and more accurate than relying on airport gate agents to conduct checks.

Anybody wanting to opt out can do so by advising gate agents, who then would manually scan that traveler’s passport, according to John McGinley, DIA’s aviation program manager.

DIA is the latest airport to implement facial recognition technology to support CBP, part of the Department of Homeland Security, in fulfilling a congressional order to implement better passenger screening on departing international flights. Other airports with the systems include those in Baltimore, Atlanta, Boston, Dallas, Detroit, Las Vegas, Los Angeles, Miami, Phoenix, and Salt Lake City.

Travelers insert their driver’s license into a slot or place their passport photo against a screen. Then agents instruct them to look into a camera screen, which captures their image and compares it to their ID.

Private companies and federal agencies increasingly rely on similar technology that gathers biometric information such as facial, eye and fingerprint images.

Civil liberties and privacy advocates, including members of Congress, have raised concerns about how the data is collected, who has access to it, and what happens if computer storage systems are hacked.

CBP officials are committed to privacy obligations, DIA officials said in a news release this week. The agency has limited the amount of personal information it collects in the scanning process and photos of U.S. citizens are to be deleted within 12 hours.