Stone Tree

You can usually tell which word is the one you're supposed to be identifying. That's why I always put dirty words in for that one :)

Not sure how this works since the whole point of a Captcha is to determine if what you type is correct or not and allow or deny access to a site based on that determination. If it doesn't know what the correct answer is then how can it decide to let you enter?

It knows ONE word. You have to get that one correct, then the second word it doesn't know. It wants you to tell it what that word is. But it won't know if it isn't correct, which is why you can put whatever you want in.

@Manticore,

It take at five matching words to confirm that it is the correct word. By putting in an incorrect word, it only requires the system to check the word one extra time to confirm it.

I know, but it makes me laugh. lol

Except that reCAPTCHA's been cracked and no longer keeps the spammers out.

If it's really works it would be good, but it's look like something that complicated, I don't know how much old text that you can decipher with CAPTCHA, maybe if you do that, you'll find another text that dificult to read and you must Re-CAPTCHA it again and again until you never know what it is about..