How teens' 'sexting' photos end up on paedophile websites: Thousands of images are published on sites after being stolen from Facebook and other social networks Internet Watch Foundation warned how many explicit images are uploaded They are often self-portraits by schoolgirls under pressure from boys Research by the foundation unearthed 12,000 images in just 40 hours Uncontrollable: The Internet Watch Foundation warned that once an explicit image is posted online it can be impossible to fully remove Tens of thousands of explicit self-portraits taken by teenagers are ending up on websites viewed by paedophiles. The naked or sexual pictures are often taken by girls at the request of boys in their classes and sent by mobile phone, in a practice known as "sexting." But unbeknown to the girls, these photographs may end up being passed around the school and even shared on social networking sites such as Facebook - then stolen and published on websites used by paedophiles. An earlier investigation found boys and girls as young as 13 are routinely swapping naked self-portraits. Now watchdog the Internet Watch Foundation has warned that many of these pictures are ending up online. Susie Hargreaves, chief executive of the charity, said "self-generated" pictures of children are now a major source of images used on websites viewed by paedophiles. In a search lasting just 40 hours, one of her analysts found 12,224 self-generated images of teenagers on 70 paedophilic websites. Given the speed of the investigation, the true number of stolen pictures is likely to be far higher. At a fringe event at the Conservative Party conference, Miss Hargreaves said she would like to see children taught about the dangers of sexting at school, so they understand that they might never be able to remove every copy of a picture or video that ends up online. "From our perspective, the younger people know about the risks, the better for us," she said, adding: "Take the issue of sexting - we don't like the word, but we did a small piece of research last year. One analyst spent 40 hours - that's all, 40 hours - and every time they came across a self-generated image which had been stolen and put on a paedophilic website, they counted it. In 40 hours they found 12,200 self-generated images. These are images one teenager had taken of themselves or another teenager shared, which had probably gone around the school and somewhere along the process had been stolen, uploaded and that's it. Miss Hargreaves also warned that older teenagers could themselves be in contravention of child abuse laws if they send or receive naked pictures - because the law says any such pictures of children under 18 can constitute abuse. She said: "One of the things that older young people are not aware is that if you're 16 or 17 you might think you are over the age of consent, but if you take an image it's still child sexual abuse because it's an image of someone under 18. There are so many risks they're not aware of. Children told the IWF that sexting is now considered "mundane and mainstream." One girl said she was asked for naked pictures "at least two or three times a week." Another said: "One explicit image I took ... is coming up on the first page of [search engines], which could jeopardise any future career I have or if any family or friends come across it." Emma McClarkin, a Tory MEP for the East Midlands, said: "If your daughter allows one picture of herself to get shared by a friend to a friend who then lets it go on, that picture can get stolen on so many multiple sites that it's impossible to ever get it off." Awareness: Internet Watch Foundation chief executive Sarah Hargreaves wants children to be taught about the dangers of sexting at school NSPCC chief executive Peter Wanless said: "These images are illegal, as they effectively constitute indecent images of children, and it's now becoming clear that adult sex offenders are getting hold of them. We urge all parents to discuss the risks with their children. The Daily Mail has been campaigning for an automatic block on online porn to protect children. Over-18s would be able to see adult images only if they "opt-in" after going through stringent age verification.