Users of the app receive anywhere from 20 cents to $1 for each “task” completed — in Crest’s case, a snapshot taken “while brushing your teeth with your favorite Crest product.” Users can’t double-dip; the app allows only one selfie per task.

The selfies are a good way for companies to obtain information that people can’t or don’t articulate in focus groups or other traditional research methods, said Ravi Dhar, director of the Center for Customer Insights at the Yale School of Management. For example, they could lead to an understanding of which rituals go along with certain types of consumption, he said.

Pay Your Selfie, which has been in business since last September, doesn’t require participants to have followers on a site like Instagram. In fact, users don’t have to share their images publicly at all (although they can). That makes it different from a company like Popular Pays, which offers Instagrammers the chance to post about brands like Nike in exchange for giveaways or cash.

The option of privacy suggests a greater possibility for authenticity, said Aparna Labroo, a professor of marketing at the Northwestern University Kellogg School of Management. “If the task comes up when a person is naturally engaging in a relevant activity and it’s minimally intrusive to take a selfie, they might actually capture some authentic moments.”

About 11 percent of the men in the Crest photos were shirtless, a level of comfort the brand rarely sees when it uses other tools in its research arsenal, said Kris Parlett, a senior communications manager for P.&G. Oral Care. Other research methods include recruiting volunteers to record videos of their oral care routine in their bathrooms or to brush their teeth in “insight suites,” mocked-up home bathrooms with mirrors that allow analysts to observe them.