After the first post, the first CAPTCHA.
For the visually impaired: a cartoon shows two cavemen. One holds a club as if it's a microphone, looks up at a cave drawing and says to the other cave man "Just to make sure you're not a bot: please read this".
Byline: History of Web 2.0 – Part 14. January 31st 9356 BC: the first captcha in history.
Credit: Geek and Poke