THIBODAUX, La. -- The teasing was relentless. Nude images of a 13-year-old girl and her friends, generated by artificial intelligence, were circulating on social media and had become the talk of a Louisiana middle school. The girls begged for help, first from a school guidance counselor and then from a sheriff’s deputy assigned to their school. But the images were shared on Snapchat, an app that deletes messages seconds after they’re viewed, and the adults couldn’t find them. The principal had doubts they even existed. Among the kids, the pictures were still spreading. When the 13-year-old girl stepped onto the...