Mr. Gobronidze said that blocking searches of children’s faces had been on “the road map” since he acquired the site in 2021, but the protection was fully deployed only this month after the publication of a New York Times article on A.I.-based threats to children.

Still, the block isn’t airtight. PimEyes is using age detection A.I. to identify photos of minors. Mr. Gobronidze said that it worked well for children under the age of 14 but that it had “accuracy issues” with teenagers.

It also may be unable to identify children as such if they’re not photographed from a certain angle. To test the blocking system, The Times uploaded a photo of Mary-Kate and Ashley Olsen from their days as child stars to PimEyes. It blocked the search for the twin who was looking straight at the camera, but the search went through for the other, who is photographed in profile. The search turned up dozens of other photos of the twin as a child, with links to where they appeared online.

Mr. Gobronidze said PimEyes was still perfecting its detection system.

Another public face search engine, FaceCheck.Id, does not appear to have any technical restrictions on searches of children’s faces. The site did not respond to a request for comment.

Daniel Solove, a law professor at George Washington University who specializes in privacy, said that there were larger problems with internet face search engines than searches of children. The services are creating mechanisms to “hoover up” people’s faces without their awareness or consent and making them searchable, Mr. Solove said, calling it a “massive privacy violation on a mammoth scale.”