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Comment by jvrossb | Hacker News Reader

I had just noticed that captchas were getting worse. I always thought sites should just make the user perform an operation. Display a hard to read but still legible "type the second letter of the third word". 'e' would be the correct response. There's got to be a reason this isn't done already, does someone know why?

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Parsing and responding to a question like that isn't difficult when the questions are algorithmically generated from a finite number of human-designed types.

Bots would spam your site once every 26 tries.

I was going to say don't most modern sites limit multiple attempts in succession? Then I realized that spammers have thousands of computers at their disposal so the successive attempts would not come from the same IP. Shoot this is a hard problem...

Spammers have thousands of machines.

More than that, since they would guess one of {e,t,o,i,n}.

It assumes that the user reads English fluently.

Or how about short stories, something like; "Brian came home very late. He couldn't find Mr. Hat. While he was thinking where his cat might be, he noticed the window was wide opened." What's the name of the cat?

I don't know if it's hard or easy to guess it algorithmically.

The problem is generating enough unique questions. If you only have 10 questions, they can just hard-code them.

That was the problem with all the "kitten captchas" etc. Very limited image database.

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