The facial-recognition app Clearview sees a spike in use after Capitol attack.

After the Capitol riot, Clearview AI, a facial-recognition app used by law enforcement, has seen a spike in use, said the company’s chief executive, Hoan Ton-That.

“There was a 26 percent increase of searches over our usual weekday search volume,” Mr. Ton-That said.

There are ample online photos and videos of rioters, many unmasked, breaching the Capitol. The F.B.I. has posted the faces of dozens of them and has requested assistance identifying them. Local police departments around the country are answering their call.

“We are poring over whatever images or videos are available from whatever sites we can get our hands on,” said Armando Aguilar, assistant chief at the Miami Police Department, who oversees investigations.

Two detectives in the department’s Real Time Crime Center are using Clearview to try to identify rioters and are sending the potential matches to the F.B.I.’s Joint Terrorism Task Force office in Miami. They made one potential match within their first hour of searching.

“This is the greatest threat we’ve faced in my lifetime,” Mr. Aguilar said. “The peaceful transition of power is foundational to our republic.”

Traditional facial recognition tools used by law enforcement depend on databases containing government-provided photos, such as driver’s license photos and mug shots. But Clearview, which is used by over 2,400 law enforcement agencies, according to the company, relies instead on a database of more than 3 billion photos collected from social media networks and other public websites. When an officer runs a search, the app provides links to sites on the web where the person’s face has appeared.

In part because of its effectiveness, Clearview has become controversial. After The New York Times revealed its existence and widespread use last year, lawmakers and social media companies tried to curtail its operations, fearing that its facial-recognition capabilities could pave the way for a dystopian future.

The Wall Street Journal reported on Friday that the Oxford Police Department in Alabama is also using Clearview to identify Capitol riot suspects and is sending information to the F.B.I. Neither the Oxford Police Department nor the F.B.I. has responded to requests for comment.

Facial recognition is not a perfect tool. Law enforcement says that it uses facial recognition only as a clue in an investigation and would not charge someone based on that alone, though that has happened in the past.

When asked if Clearview had performed any searches itself, Mr. Ton-That demurred.

“Some people think we should be, but that’s really not our job. We’re a technology company and provider,” he said. “We’re not vigilantes.”