We have all run into CAPTCHAs (those little squiggly words we must type to access web services). You might also know there are multiple projects under way with the goal of scanning books and documents into digital form. Now imagine combining these two concepts!
Enter reCAPTCHA, whose goal it is to provide login security AND help digitize thousands of books. Every time a user uses reCAPTCHA to log into a website, they are also asked to decrypt a “hard to read” word from one of the book digitizing projects. So as you log in to a website, you are helping digitize a book. Check out THIS ARTICLE discussing reCAPTCHA in more detail.