WASHINGTON — The program makes boarding an international flight a breeze: Passengers step up to the gate, get their photo taken and proceed onto the plane. There is no paper ticket or airline app. Thanks to facial recognition technology, their face becomes their boarding pass.

“I would find it superconvenient if I could use my face at the gate,” said Jonathan Frankle, an artificial intelligence researcher at M.I.T. studying facial recognition technology. But “the concern is, what else could that data be used for?”

The problem confronting Mr. Frankle, as well as thousands of travelers, is that few companies participating in the program, called the Traveler Verification Service, give explicit guarantees that passengers’ facial recognition data will be protected.

And even though the program is run by the Department of Homeland Security, federal officials say they have placed no limits on how participating companies — mostly airlines but also cruise lines — can use that data or store it, opening up travelers’ most personal information to potential misuse and abuse such as being sold or used to track passengers’ whereabouts.