In wakfu if you farm up to much you get spawned into a special zone where you need to beat captchacat in very simple game. You need to press on 3 fields to win (the one that cat has). Bots cant solve this riddle it seems and if they keep failing they get a gathering debuff (and probaly a ban after if they fail to much). Players however get rewarded by 40 resorce and some cash if the solve the puzzle.
Now lets say we place a similar game in wow.
If you overfarm (number is random), you will get summoned into a special zone. In this zone you need to press randomly generated buttons on screen (lets say button 1A, 4B, 6C). If you win you get 1500 gold, 50 ore (if you farm ore) and a small chance of epic of your lvl that you can use.
If you fail...24 hour debuff and for each fail you get extended by 24 hours till you hit 7 days wich triggers automatic ban (nobody can be that stupid).
You get rid of a debuff till you beat the game again. The chance to encounter the *game* is higher as the larger you debuff is.
And its also time limited, so if you have a bot on a farming run for 6 hours, when you go to sleep, he will surely broke or even ban you.
Something like this would probaly be to hard:
...also colorblind person would be at disadvantage.