What can be more clear than this?
If anything, I'd prefer to have the king I'm supposed to checkmate standing on a red field to make it easier to spot.
My point is that, while the one-liner captures the idea of the captcha, the summary doesn't explain how to actually execute.
Starting with "Hey, let's solve a CAPTCHA because I'm not sure if you are a human" and burying information which side the user is supposed to play somewhere in the middle of the text would make it a major PITA.
My point is that, while the one-liner captures the idea of the captcha, the summary doesn't explain how to actually execute.