The same image is presented to other Google users around the world at the same time. If enough people submit the same number, Google accepts they have accurately read the photo and are therefore not bots.

Traditionally these security checks – of which there are estimated 200 million a day - have involved typing blurred letters or words into a box.

According to the U.K. Big Brother Watch's delightfully named Nick Pickles, this constitutes "a serious privacy issue with identifying the individual number of people's homes."

It is also an instance of Google being "underhand and crude," according to Mr. Pickles, as the company is essentially using the public as "unwitting data loggers."

Google claims there is no security risk, as the photos presented in CAPTCHAs are cropped and visible from public motorways. As Google's spokesperson told the Guardian, "We often extract data such as street names and traffic signs from Street View imagery to improve Google Maps with useful information like business addresses and locations."