Schoolgirls are unwittingly exposing themselves to paedophiles by posing for explicit photographs and posting them on the internet, a south Wales school warned this week.

The warning came as a 31-year-old man was jailed for having “cybersex” with a 14-year-old via the internet in Scotland.

Staff at Cefn Hengoed school in east Swansea say two girls, in separate incidents, took indecent photographs of themselves in their homes without realising how widely they could be circulated via the web.

Assistant head Heather Cooper said the first case three months ago involved a 14-year-old girl who took naked pictures of herself using a digital camera and transmitted them online via an instant messaging service.

Earlier this month, a 13-year-old girl sent photos of herself in underwear with handcuffs and a whip via a webcam to an internet site. The photos were widely accessed by other pupils and caused a fight on school grounds.

Mrs Cooper said: “When we called in this girl’s parents they were absolutely devastated - they thought she was using the computer for homework. Many parents are allowing their children access to computers without being supervised.”

She added that one girl did it for a dare, while the other initially called it “a bit of fun”.

The 730-pupil school is now working with police on an education programme for pupils and is set to advise parents against giving children computers in their bedrooms. A letter home will advise parents to monitor their children’s internet use, including the websites visited and who they contact.

It decided to publicise the incidents in order to warn other schools and families of potential dangers.

Deputy head Geoff Brookes said: “The girls were clever enough to do it, but not to work out what it meant for their image and how it could be abused.

“We have an obligation to protect children who do these things really very innocently - that is far more important than worrying about the reputation of our school.”

Anna Brychan, director of the National Association of Head Teachers Cymru, welcomed the fact that parents and pupils were being warned of new dangers.

“Pupils are skilled at using technology but may not appreciate its impact. These are the kinds of experimentations that pupils have always done but these days they can have far greater exposure at just the click of a button.”

Sara Reid, assistant children’s commissioner for Wales, said: “Parents need to ensure they are computer literate, rather than leaving the IT knowledge to their children.

“The danger is that children and young people experience the internet as being a private world where they can have friendships and conversations, whereas in reality it’s a public space. That message needs to get across.”

Brian Lightman, national executive member of the Secondary Heads Association, said: “Schools can educate children about abuse of the internet, but it’s the responsibility of parents to monitor what their children are doing when on the internet.”

Superintendent Pat Tucker, of the South Wales Police community safety department, said similar instances had happened but were