CAPTCHAs, also known as the annoying security questions you decipher to convince a webpage that you’re a human, are used to stop fraudulent online activity. But have you ever noticed that some of them look suspiciously like house numbers pulled from Google Street View, or bits of text from books and newspapers?

A CAPTCHA, for those unfamiliar, is the distorted text meant to stop bots from signing up for online accounts. It stands for Completely Automated Public Turing test to tell Computers and Humans Apart. But did you know that internet users, such as you, are being used to identify unknown bits of information from Google Street View, or online texts, that cannot be scanned or verified by other means? Every time you enter a CAPTCHA — one that looks like a bit of text from a book, or a street number, Google uses that data to verify the image against other information, which will then be used to improve data on online services like Google Maps.

Says Google: “We’re running an experiment in which characters from Street View images are appearing in CAPTCHAs. We often extract data such as street names and traffic signs from Street View imagery… Based on the data and results of these tests, we’ll determine if using imagery might also be an effective way to further refine our tools for fighting machine and bot-related abuse online.”