Because it is a felony to possess or distribute child pornography, the charges could be serious. But because most of the people at fault are themselves minors and, in some cases, took pictures of themselves and sent them to others, law enforcement officials are at a loss as to how to proceed. “Consenting adults can do this to their hearts’ content,” said Thom LeDoux, the district attorney, but “if the subject is under the age of 18, that’s a problem.”

He added that he was not interested in arresting hundreds of children and would “use discretion” if he decided to file charges.

Mr. Welsh said a significant percentage of the student body at Cañon City High School had participated, with boys and girls involved in seemingly equal numbers. The photo-sharing, some of which took place in school, was done largely on cellphone applications called “vault apps” that look innocent enough — some look like calculators — but are really secret troves of photographs accessible after entering a password.

While sexting among children is a rampant problem, “I hope no other school has it at the level we have it at,” Bret Meuli, the principal of Cañon City High School, said in an interview in his office. “But I fear we aren’t the only ones.”

Students at the school described a competitive point system that classmates used to accrue photographs. Different point values were assigned to different students. Students who collected naked photographs gained points by adding these desirable children to their collections. Isaac Stringer, a junior interviewed outside the high school who said he did not participate in the photo-sharing, called the boy with the largest collection “the pimp of pictures.”