Why do I have to tell the computer that I'm not a robot?

“Sometimes when I’m online, a website will ask me to type in a bunch of weird letters and numbers, or pick out all the pictures that have a car or a street sign, or just click a box that says ‘I’m not a robot’ before it lets me go any further. Why does this happen?”

These are a few different examples of a CAPTCHA, an acronym that stands for “completely automated public Turing test to tell computers and humans apart.” According to Architects of the Information Age, edited by Robert Curley, the CAPTCHA was developed in 2000 by computer scientists at Carnegie Mellon University. Yahoo requested their help keeping bots (which are automated computer programs) out of their chat rooms. The bots were collecting personal information and filling the rooms with spam. However, the programs couldn’t recognize distorted text. By asking users to identify twisted or crossed-out letters before they could enter the chat, Yahoo ensured that only people, not bots, could enter their chat rooms.  

The official CAPTCHA website gives us a few more examples of what it does. It can prevent bots from sending spam comments, stuffing the ballot boxes of online polls, and slowing down email services by signing up for thousands of accounts at a time. If you forget your email password and have to make a few guesses, the site may ask you to solve a CAPTCHA. This protects your account by keeping bots from running through every possible password until they get in.

There are ways to circumvent CAPTCHA. Artificial intelligence has gotten good at solving the ones that are only text, which explains why newer CAPTCHAs can involve images. There are also CAPTCHA solving services, where workers are paid approximately fifty cents to a dollar for every thousand CAPTCHAs they solve.