If you’ve ever tried to create an account or leave a comment on most websites, you’ve likely been stopped by a CAPTCHA image. CAPTCHAs are the annoying little strings of numbers and letters that websites ask you to read in order to verify that you are a human. And, while everybody can agree that trying to read what seems like Greek symbols off of a tiny screen is very frustrating, most people don’t realize that there is actually a deeper purpose to these images.

In his TED talk, Luis von Ahn, one of the creaters of the CAPTCHA and a founder of the sebsequent program ReCAPTCHA, talks about how filling in CAPTCHAs actually helps computers read and record old faded books, and how they’ve taken a seemingly impossible task (digitizing millions of old books and texts) and broken it down word by word among the billions of people on the internet each day.

For more information, click here to view a transcript of Luis’ TED talk on the subject, and learn how each day you contribute to a world-scale project that you didn’t even know existed!