CAPTCHAs – the questions that a website asks you to answer to prove if you’re a human being or not – come in many shapes and forms.

Conventional CAPTCHA

Although they most commonly ask you to decipher some words hidden in a distorted graphic, there are more elaborate versions which can ask you tosolve some complicated mathematical calculation or ask you to add toppings to a pizza in an attempt to stop automated bots leaving spammy messages.

As a keen chess player, I was interested to see this CAPTCHA being used on an online chess forum:

Chess CAPTCHA

Okay, so it’s not much of a challenge if you’re a chess player, but it also clearly locks out any users who do not know how to play chess. (For those of you can’t see the checkmate, the answer is upside-down at the bottom of this article – and make sure to realise that Black is playing from the bottom)

But most importantly, if a CAPTCHA system like this were to become widely-used, how tricky would it be for an automated bot to solve the puzzle?MORE