Stancl told the court he had been taking medication for depression

A US teenager who blackmailed fellow students at his secondary school into having sex after using their Facebook images has been convicted.

Anthony Stancl, 19, from Wisconsin, admitted two counts of sexual assault and in return other more serious charges were dropped.

Prosecutors said he tricked boys into sending naked images of themselves, and then blackmailed the boys for sex.

Stancl, who said he had been depressed, faces up to 50 years in jail.

The case came to light after a 16-year-old pupil told the authorities he was being blackmailed.

After exchanging explicit pictures of himself with Stancl - who prosecutors said posed as a girl online - when he was 15, the boy had been told the images would be distributed around the school if he refused to perform sex acts.

The boy's images were among about 300 such pictures and videos of more than 30 male students at New Berlin Eisenhower High School, in south-east Wisconsin, that police found on Stancl's computer.

Waukesha County district attorney Brad Schimel said he was satisfied with the plea deal, which spared victims from having to appear in court - a key factor in his negotiations, the Associated Press news agency reported.

"I've never had a case where the victims and their families were more apprehensive about testifying," Mr Schimel was quoted by AP as saying.

"From the victims' perspective, they're relieved we're doing this."