On a recent Thursday morning in Queens, travelers streamed through the exterior doors of La Guardia Airport’s Terminal C. Some were bleary-eyed — most hefted briefcases — as they checked bags and made their way to the security screening lines.

It was business as usual, until some approached a line that was almost empty. One by one, they walked to a kiosk with an iPad affixed to it and had their photos taken, as a security officer stood by. Within seconds, each passenger’s image was matched to a photo from a government database, and the traveler was ushered past security into the deeper maze of the airport. No physical ID or boarding pass required.

Some travelers, despite previously opting into the program, still proffered identification, only for the officer to wave it away.

This passenger screening using facial recognition software and made available to select travelers at La Guardia by Delta Air Lines and the Transportation Security Administration, is just one example of how biometric technology, which uses an individual’s unique physical identifiers, like their face or their fingerprints, promises to transform the way we fly.

This year could be the “tipping point” for widespread biometrics use in air travel, said Henry Harteveldt, a travel industry analyst for Atmosphere Research. Time-consuming airport rituals like security screening, leaving your luggage at bag drop and even boarding a plane may soon only require your face, “helping to reduce waiting times and stress for travelers,” Mr. Harteveldt said.

In the United States, major airlines have increasingly invested in facial recognition technology as have government agencies in charge of aviation security. Overseas, a growing number of international airports are installing biometrics-enabled electronic gates and self-service kiosks at immigration and customs.

The technology’s adoption could mean enhanced security and faster processing for passengers, experts say. But it also raises concerns over privacy and ethics.

Dr. Morgan Klaus Scheuerman, a postdoctoral researcher at the University of Colorado who studies the ethics of artificial intelligence and digital identity, said many questions have emerged about the use of biometrics at airports: How are the systems being trained and evaluated? Would opting out be considered a red flag? What if your documents don’t match your current appearance?

“I’m sure many people feel powerless to stop the trajectory,” Dr. Scheuerman said.

In the United States, bullish about the technology

The T.S.A., with more than 50,000 officers at nearly 430 airports in the United States, is the main federal agency ensuring the safety of the hundreds of millions of passengers who fly each year. Travelers who are determined to be “low-risk” can apply for T.S.A.’s PreCheck program, which offers expedited security screening at more than 200 domestic airports. PreCheck, which requires an in-person appointment to show documents and give fingerprints, and biometric verification by Clear, a private screening company, have helped to reduce the wait time for screening, but air travelers still must occasionally stand in long queues to get to their gates.

The T.S.A. has experimented with facial recognition technology since 2019. Screening verification currently offered at Denver and Los Angeles International Airports and some 30 other airports starts when a photo is taken of the traveler. Then facial recognition software is used to match the image to a physical scan of a license or passport. The photo is deleted shortly afterward, according to the agency. This process, which passengers can opt out of, will be available at some 400 more airports in the coming years, the agency said.

Melissa Conley, a T.S.A. executive director overseeing checkpoint technologies, said that biometric technology is better than human agents at matching faces rapidly and accurately.

“People are not good at matching faces. It’s just known,” Ms. Conley said. “Machines don’t get tired.”

The process still requires passengers to show their IDs. But the program being tried by Delta, called Delta Digital ID, changes that.

With Delta Digital ID, PreCheck travelers can use their faces in lieu of boarding passes and ID at both bag drop and security at La Guardia and four other airports, including John F. Kennedy International Airport and Hartsfield-Jackson Atlanta International Airport.

Facial recognition shaves more than a minute off bag drop, to roughly 30 seconds, and reduces the security interaction from 25 seconds to about 10 seconds, said Greg Forbes, Delta’s managing director of airport experience. While a “simple change,” the time savings add up, making the line noticeably faster, Mr. Forbes added.

“Anywhere that there’s PreCheck, I think, could benefit from Digital ID,” Mr. Forbes said.

Other airlines have begun similar experiments for PreCheck travelers: Those flying on American Airlines can use their faces to get through PreCheck screening at Ronald Reagan Washington National Airport and also to enter the airline’s lounge at Dallas-Fort Worth International Airport. United Airlines allows PreCheck travelers to use their faces at bag drop counters at Chicago O’Hare International Airport; the airline is scheduled to bring this program to Los Angeles International Airport in March.

And Alaska Airlines plans to spend $2.5 billion over the next three years in upgrades, including new bag drop machines, in Seattle, Portland, Ore., San Francisco, Los Angeles and Anchorage. A machine will scan the traveler’s ID, match it to a photo, and then scan the printed bag tags. The new system, designed to move guests through the bag tagging and dropping process in less than five minutes (compared to around eight minutes now), will be in Portland in May.

Charu Jain, the airline’s senior vice president of innovation and merchandising, said that it felt like the right moment for Alaska because of improved technology and increasing passenger familiarity with facial recognition.

At the borders

The fastest growing use of facial recognition software at U.S. airports so far has been in security measures for entering and exiting the United States.

The growth stems from a 2001 congressional mandate, in the wake of 9/11, requiring the implementation of a system that would allow all travelers arriving and departing the United States to be identified using biometric technology.

Overseen by the Customs and Border Protection agency, the biometric system for those entering the United States is in place, and scanned 113 million entries at airports last year. For those leaving the country, the system is available at 49 airports, with the C.B.P. aiming to cover all airports with international departures by 2026.

Biometric entry is mandatory for foreign nationals. But biometric exit is currently optional for these travelers, while C.B.P. is making the system fully operational. At any border, the biometric process is optional for U.S. citizens, who can instead request a manual ID check.

Diane Sabatino, acting executive assistant commissioner for field operations at C.B.P., said that the system aims to improve security, but she acknowledged rising privacy concerns. Images of American citizens taken during the process are deleted within 12 hours, she said, but photos of foreign nationals are stored for up to 75 years.

“We are not scanning the crowd looking for people,” she said. “It’s certainly a privacy issue. We are never going to ask them to sacrifice privacy for convenience.”

Miami International Airport, the second busiest airport in the United States for international passengers last year, has one of the “largest deployments” of biometrics in the country, airport executives say. In a partnership with SITA, a global information technology provider for the air transport industry, the airport has installed the technology for departing passengers at 74 out of 134 gates and plans to cover the remaining gates by the end of this year, said Maurice Jenkins, chief innovation officer at Miami-Dade Aviation Department.

The contract with SITA costs $9 million, but Mr. Jenkins said that the new technology was increasing efficiency in the rest of the airport’s operations, such as fewer gate agents checking documents.

Document-free travel overseas

Experts believe the future of air travel is one where facial recognition will be used throughout the entire airport journey: bag drop, boarding, even entering lounges and purchasing items at retail stores within the airport. It may be so streamlined that security checkpoints could be eliminated, replaced instead by security “tunnels” that passengers walk through and have their identity confirmed simultaneously.

“This is the future,” said Dr. Sheldon Jacobson, a computer science professor at University of Illinois at Urbana-Champaign who researches aviation security.

According to a recent report by SITA, in which 292 airlines and 382 airports around the world were surveyed, 70 percent of global airlines are expected to use some sort of biometric identification by 2026 and 90 percent of airports are currently investing in the technology.

More comprehensive experimentation has already landed at some airports abroad. Later this year, Singapore’s Changi Airport intends to go passport-free for departures; all passengers, regardless of nationality, will be able use this system. At Frankfurt Airport in Germany, passengers can now use their faces from the time they check-in to boarding. The airport is installing biometric technology throughout its two terminals and making it available to all airlines.

In China, 74 airports — 86 percent of the country’s international airports — have biometric technology in place, according to a report released last month by the global market research company Euromonitor and the U.S. Travel Association. At Beijing Capital International Airport, the country’s busiest airport, travelers can use facial recognition throughout their entire journey, even to pay for items at duty-free shops.

But in the United States, according to the report, only about 36 percent of international airports have some biometric capabilities.

There are several reasons for the country’s lagging adoption, said Kevin McAleenan, the former acting secretary for the U.S. Department of Homeland Security and currently chief executive of Pangiam, a travel technology company. Simply, the United States has many airports and the immigration exit process here is different from other places.

At many airports overseas, the government controls immigration for departing travelers, allowing these airports to have a government-established biometric system.

In the United States, airlines, using C.B.P. passenger data, confirm the identities of travelers leaving the country.

Concerns over government surveillance

Biometrics use has already seeped into daily life. People unlock their phones with their faces. Shoppers can pay for groceries with their palms at Whole Foods.

But critics believe that the technology’s convenience fails to outweigh a high potential for abuse — from unfettered surveillance to unintended effects like perpetuating racial and gender discrimination.

Cody Venzke, senior policy counsel on privacy and technology at the American Civil Liberties Union, said the government had not yet shown a demonstrated need for facial recognition technology at airports and worried about a “nuclear scenario.”

“Facial recognition technology,” he said, could be “the foundation for a really robust and widespread government surveillance and tracking network.”

“That technology might be able to be used to track you automatically and surreptitiously, from place to place, as you go about your day, and create a really detailed mosaic about everything about your life,” Mr. Venzke said.

The A.C.L.U. supports a congressional bill, introduced last November, called the Traveler Privacy Protection Act. Listing concerns over security and racial discrimination, the bill would halt the T.S.A.’s ongoing facial recognition program, and require congressional authorization for the agency to resume it.

Ms. Conley, of the T.S.A., said that a stop in the agency’s biometrics efforts would “take us back years.”

For some travelers, facial recognition has already become a reliable tool. At J.F.K. on a recent afternoon, Brad Mossholder, 45, used Delta’s Digital ID line to breeze through the security screening at Terminal 4 and bypass a dozen travelers in the adjacent PreCheck lane.

He was flying from his home in New York to San Diego for his job in corporate retail, and as a frequent business traveler, has used facial recognition several times. The process is faster and easier overall, Mr. Mossholder said, and he wasn’t worried about privacy.

“Honestly, my photo is on LinkedIn, it’s on a million social media sites,” he said. “If you really wanted to see a picture of me, you could.”

Follow New York Times Travel on Instagram and sign up for our weekly Travel Dispatch newsletter to get expert tips on traveling smarter and inspiration for your next vacation. Dreaming up a future getaway or just armchair traveling? Check out our 52 Places to Go in 2024.