Chances are that at some point when searching Google, purchasing concert tickets, or signing up for a forum, you've had to click a few boxes to confirm your humanity. But while these CAPTCHA tests are usually meant to keep robots out, one website is welcoming them in. 

The conceit of Humans Not Invited is essentially a reverse CAPTCHA. Visitors to the site are greeted with a vision test not unlike the ones you've done before, but instead it's filled with seemingly indistinguishable blue and gray blurry boxes. When I tried, I was prompted to "select all squares with selfie sticks."

Most humans, like me, will fail to decipher the hidden selfie sticks and will be shown a message that says "YOU'RE A HUMAN. YOU'RE NOT INVITED." 

To the human eye these boxes appear indistinguishable, a specially programmed bot can spot out the correct image simply by identifying a handful of pixels, according to the project's creator, Damjanski, (his real name is Danjan Pita).