You have memorised your passwords and your PIN is secret, now it is the house keys that must be hidden from prying eyes.

Using only a camera, a computer and a key-cutting machine, scientists have duplicated sets of keys after taking snaps of them from more than 60 metres away.

Computer experts at the University of California in San Diego set out to show how easily keys could be copied from a digital image to highlight the potential security risk of leaving keys on display.

At a computer conference in Alexandria, Virginia, Stefan Savage, a computer security expert who led the "Sneakey" project, surfed the photo-sharing website Flickr and found pictures that clearly showed peoples' keys, even if personal information in the shots had been blurred out.

In one demonstration, the team cut duplicate keys after analysing images taken on a mobile phone. In another, they used a telephoto lens to take pictures of a set of keys on a cafe table from the roof of a university building.

The software re-orients images of keys and determines the dimensions of the peaks and notches that connect with a lock's mechanism. Then the information can be plugged into a key-cutting machine to produce an exact replica.

"We built our key duplication software system to show people that their keys are not inherently secret," Savage said. "Perhaps this was once a reasonable assumption, but advances in digital imaging and optics have made it easy to duplicate someone's keys from a distance without them even noticing."

Experts have been able to copy keys by hand from high-resolution photographs for some time, but Savage believes that cheap digital cameras and computer software mean almost anyone with basic technological know-how could do it.

"If you go onto a photo-sharing site such as Flickr, you will find many photos of people's keys that can be used to easily make duplicates. While people generally blur out the numbers on their credit cards and driver's licences before putting those photos on-line, they don't realise that they should take the same precautions with their keys," Savage said.