We've officially reached the point where humans have to prove they're, well, human just to access websites. One of the most common ways to do this? CAPTCHA. CAPTCHA stands for Completely Automated Public Turing test to tell Computers and Humans Apart. It might sound long-winded, but the idea is simple. Computers still struggle to crack these tests, making them a solid way to block bots. But why exactly do they work so well?