SAN FRANCISCO — Like many parents, Yvonne Meré was deeply disturbed when she read about a frightening new trend. Boys were using “nudification” apps to turn photos of their female classmates into deepfake pornography, using images of the girls’ faces, from photos in which they were fully clothed, and superimposing them onto images of naked bodies generated by artificial intelligence. But unlike many parents who worry about the threats posed to their children in a world of ever-changing technology, Meré, the mother of a 16-year-old girl, had the power to do something about it.