US Customs and Border Protection (CBP) continued its federally mandated implementation of facial recognition biometric exit technology at US airports this week with new deployments at Las Vegas’ McCarran International Airport (LAS) and Houston’s William P. Hobby International Airport (HOU).

Beginning Aug. 8, CBP began deploying facial recognition technology on one daily flight from the Las Vegas to Guadalajara, Mexico, and also “select flights from HOU.” CBP did not identify the airlines involved in the program at either airport, and at Houston Hobby, CBP did not specify the routes.

CBP began biometric technology deployments at Houston’s George Bush Intercontinental Airport (IAH) and at Washington Dulles (IAD) in June, followed by Chicago O’Hare (ORD) in July. CBP originally tested the technology at Hartsfield-Jackson Atlanta International Airport (ATL) in June 2016, as part of a DHS mandate issued in July 2015 to create a biometric entry and exit system to record the arrival and departure of “certain aliens.”

As described by CBP, “using the flight manifest, CBP builds a flight specific photo gallery using photographs from the travel document the traveler provided to the airline. CBP then compares the live photo against the document photo in the gallery to ensure the traveler is the true bearer of the document. If the photo captured at boarding is matched to a US passport, the traveler—having been confirmed as a US citizen—is automatically determined to be out of scope for biometric exit purposes and the photo is discarded after a short period of time.”

“Through our consultations with the airlines and airport stakeholders, and based on the success of several pilots, CBP determined that facial recognition was a viable exit solution,” CBP deputy executive assistant commissioner-office of field operations John Wagner said.

CBP is also working directly with US airlines to integrate biometrics into their boarding processes, including Delta Air Lines’ testing of eGates at New York-JFK and ATL, as well as biometric fingerprint boarding at Washington Reagan National Airport (DCA). New York-based JetBlue Airways is testing facial recognition technology at Boston-Logan that enables passengers to self-board without scanning a boarding pass.

CBP plans to continue biometric deployment at other US airports through the summer, with Los Angeles International, San Francisco International, Miami International, Newark Liberty and Dallas/Fort Worth airports under consideration.