Teenage girls have been warned not to send indecent pictures to their boyfriends after a number of snaps turned up online.

North Herts chief inspector Julie Wheatley revealed there have been several reports from concerned parents whose daughters were coaxed into sending indecent photos.

The images – which are illegal if the girl is under 18 – have then been posted on public websites after the relationship ended.

Mrs Wheatley told the Mercury: “It concerns the parents and the girls affected massively. I just want people to be aware that this is an offence.

“My officers have been going into schools to do a personal safety awareness campaign around this issue.”

In the wake of the news, The Mercury contacted all of the secondary schools and colleges in the district for comment. Only two spoke out about the issue.

Jed Whelan, head teacher of Fearnhill School in Letchworth GC, said: “We are aware of the issue around safe use of the internet.

“We make our students aware of the dangers of inappropriate use of the internet and are constantly reaffirming that. I’m sure all schools will do the same.”

Meanwhile, Martin Brown, head teacher at Hitchin Boys’ School , said: “Our PSHE programme covers all aspects of e-safety, and our e-safety policy also refers to the dangers of online communication.

“In addition, we have held evenings for parents to provide guidance on similar internet-related issues.”

As the school authority, Hertfordshire County Council (HCC) ran a survey that found fewer than 1 per cent of parents thought their children used chat rooms, although nearly 10 per cent of youngsters did.

Councillor Chris Hayward – cabinet member for enterprise, education and skills at HCC– said: “The council is committed to working with our partners to keep young people safe both on and offline.

“By talking to them about what is appropriate to share with others we can do our best to help protect them from potential dangers.”

Claire Lilley, NSPCC lead for child safety online, said: “Young people may think ‘sexting’ is harmless but it can mean they are committing a crime.

“It may also leave them vulnerable to blackmail and bullying and the humiliation and embarrassment of everyone they know seeing the images.

“There is also the risk that sexual predators will try to get hold of the images, which we know is a very real risk.”

The charity said the problem was becoming more prevalent and that it had held 351 counselling sessions with affected children in 2012/13 – an increase of 28 per cent on the previous year.

In a statement issued to this newspaper, Hertfordshire Constabulary warned that posting the photos online is a criminal offence that is taken very seriously, and that those responsible would be pursued.

Police are advising young people to be mindful of privacy settings when sharing information online, to only share details such as mobile numbers with trusted friends, and never to send indecent images.