It will lose its usefulness once it's in wide use. If you run a small site that is not directly targeted by spammers, just add an additional form field and ask a very simple question like 1+1= or ask the user to leave the field empty.
Give it an obvious name like "username" so that the bot will "know" what to do. Hide the textfield with CSS so that non-visual impaired people don't even need to bother with this.
Easy to implement, but useful.

BRILLIANT! (And it gives me a useful headache, just to look at.)

I don't really get it... Is that like a hidden field in a form? (designed for robots)

Don't doubt the stupidity of some web-users.

i can't use some site commenting service because most times i cant find out what's written in the image -_-' ... i'm really considering the fact i am a program and not human...

I'm sure someone will take the time to enter that nonsense. I entered 4 or 5 Google captchas in a row because they were unclear.

eioeowoijfnn2eo357ieoiew
weopifweqolc7wlksdopiwe
wepewewpo78ej52pcnipweq
weiopediopeo23ijeiojd
ediopewjewjoiweoieowejewdow
wepoidjeopied1oieoiooimxcio
32oweonddoio456566dewew

That means I´m a robot? I passed Voight-Kamp test.

lol. Hope this captchas is just a joke ;-) (even "captchas" is hard to write!)

N i c e S i t e!

eioeowoijfnn2eo357ieoiew
weopifweqolc7wlksdopiwe
wepewewpo78ej52pcnipweq
weiopediopeo23ijeiojd
ediopewjewjoiweoieowejewdow
wepoidjeopied1oieoiooimxcio
32oweonddoio456566dewew

Aah, nexus6 beat me to it!

habrahabr ;-)

What does Google think of hidden fields used by CSS?

Why would you want to hide a field by CSS when you can just use the hidden type for input?

<input type="hidden" id="example"....

I guess because CSS is harder to parse... there's so many ways something can turn invisible... filter: alpha(opacity=0) etc. ...

simply... 7

haha, nice one!

It's a good idea...
Maybe you can send computers to an infinite loop asking them the meaning of life. They won't bother for some years, till they discover the answer to life, the universe and everything is 42.

42

Damn Zim! You got there just before me! I was was inpired by MarcoSZone

Lol, funny

Nexus6: "I passed Voight-Kamp test."
Brilliant

Very nice post/reply set!

What about the aliens ? Will they be able to decipher this powerfull code ?

[Signature removed]

Roger, your's looked more like spam, so you get an extra rep point from me ;)

Nice job :)

Ernesto Schutz

code for bot:
--------------
if(recognizedText.Length() > 10){
   dontEnterInBox();
else
   enterInBox();
------------
sorry to destroy your dreams ;)

http://www.timtucker.com/weblog/?p=74 has been implemented here

One workable variation of this idea would be a captcha that says something like:
"Enter three pluses in the captcha field"