While the @YesYoureRacist account was one of the most visible leaders in the name-and-shame effort, it also made a misstep. The account apologized for using an old photo of Joey Salads, a YouTube star, from a different event in which Mr. Salads said he was wearing an armband with a swastika as an “experiment.” He was not at the rally. And the person behind @YesYoureRacist — who could not be reached for comment — was the target of an apparent doxxing by another Twitter user, who posted what appeared to be phone numbers and other personal information. Twitter deleted that tweet and suspended the account.

As news organizations have learned — sometimes through high-profile mistakes — misidentifying a person accused of wrongdoing can have bad consequences, from lawsuits to a loss of credibility.

Journalists at Storyful, a news agency that verifies social media content, aim to find eight to 10 pieces of corroborating information before confirming an identity, said Ben Decker, a research coordinator. Identification must be approved by several editors, he said. (The New York Times is a Storyful client, and Mr. Decker works directly with The Times.)

Simply looking at a photo can often lead to mistakes. There’s a lot of potential for human error related to lighting, positioning, how much of the face is seen, and how many similar faces are in the world, Mr. Decker said.

Having a name isn’t enough, either. For example, there are several men with military backgrounds in the United States named James Alex Fields, the name of the man charged in Saturday’s fatal attack with a car on protesters in Charlottesville, Mr. Decker said. An attempt at confirming an identity in that case would have required a date of birth and address, at least.

As for Mr. Quinn, the University of Arkansas professor, he fell victim to a resemblance to one of the rally participants, but the possibility that he was there wouldn’t have held up with more careful checking, Mr. Decker said. Such mistakes routinely happen during amateur sleuthing, he said.

“There’s ostensibly a very quick jump into the first detail that emerges,” he said.

People who then try to correct the record often feel drowned out by the false information.