File photo: The app, called Gallery Guardian and due to be launched this month, scans images as they are created or received to detect naked skin, genitalia or breast exposure. Picture: AP

It's a modern craze that terrifies parents the world over.

But finally they have been given a tool to fight back against the alarming and potentially dangerous phenomenon of "sexting" – when mobile users, often children, send sexually explicit messages and images of themselves.

A new app uses sophisticated image-recognition algorithms to identify inappropriate pictures that appear on a child’s mobile phone – and immediately alerts a parent when anything suspicious is detected.

The app, called Gallery Guardian and due to be launched this month, scans images as they are created or received to detect naked skin, genitalia or breast exposure.

Seconds after potentially offensive content appears on a child’s smartphone – already synced to their parents’ device – a message is sent to the adult, reading: "Suspicious Image Detected."

Parents are then able to take the phone from the child to investigate the photo – or alert an adult nearby if the child is away from home.

Android phone users will not only be told when a suspicious photograph has been sent or received, but also what method it has come by, for instance from programs such as WhatsApp or Snapchat, or if it has been downloaded from the internet – possibly from a pornography website.

The app on Apple phones will not provide the same level of detail, with parents simply told when the "suspicious" picture arrived in the device’s photo gallery. Because it is illegal to share images of child porn, the app does not copy suspicious pictures to the parents. Gallery Guardian enables parents to synchronise up to six devices.

It is the brainchild of Daniel Skowronski, 50, a father-of-four including a 12-year-old daughter, from Hampstead, North London. "I realised how widely children as young as eight were sharing these inappropriate images," said Mr Skowronski, founder of YIPO Technologies, which specialises in photo-recognition technology.

"Boys are saying to girls right now, 'If you don’t send me something I’m not going to ask you out.' It’s ridiculous to imagine the world they’re living in right now.

"This app brings parents peace of mind that there is technology working for them and watching everything their child is doing. It’s all about putting power back into the parents’ hands."

Child protection campaigner Pippa Smith said: "New technology that can help parents keep an eye and give their children more guidance sounds like a good thing.

"But ultimately, reducing sexting can’t just be left to technology. Children need to know it is wrong and why. However, they do not have the cognitive maturity to resist this sexualised culture."