A hacker has managed to install a facial recognition program on Google Glass, allowing the device to identify people's faces, despite Google's insistence that Google Glass could not be used to violate people's privacy.

Stephen Balaban, founder of Lambda Labs in San Francisco, said he had managed to circumvent the Google operating system for the device, and install software that used Google Glass's forward-mounted camera.

"Essentially what I am building is an alternative operating system that runs on Glass but is not controlled by Google," Balaban told NPR.

Concerns have been voiced about the technology being used to violate privacy, and earlier this year US Congress's Bi-Partisan Privacy Caucus and representatives of 10 international data protection agencies wrote to Google, urging it to tighten its privacy policy.

The Palo Alto-based company refused, but instead altered its development policy to prevent face-recognition technology from being installed on the head-sets, or so it claimed.

It has also proposed features designed to make it obvious when a Glass user is, for example, taking a picture, by making it necessary to issue a voice instruction or other explicit commands.

The tech giant also claims it will be able to block unapproved apps and software. But already, the company's road-blocks appear to have been circumvented.

Nor is this the first time. Developer Michael DiGiovanni has installed a device called Winky, which allows users to take a photograph with the blink of an eye.

In Japan though, as questions mount over the device's capacity to redraw the line of where personal privacy starts, 'anti-Google' glasses have already been developed, using LED lights invisible to the human eye to block the Google Glass camera from photographing the human face.

In America, casinos, cinemas, strip clubs, and even some cafe and bar owners have already banned the device.

Google Glass is scheduled for launch later this year, after being issued on trial to 2,000 bloggers and technology writers. It is expected to cost around £200 in the UK.