[T. P. Pole]

So, let me see if I get this right. The amount of spam is lower today because computer robots cannot read these things, only humans. So we are going to take the human effort in reading these things and use that to teach computers how to read them, albeit for the good reason of digitizing books.

Umm, what's to stop this "learning" from passing along to the spam robots, this allowing them to pass the test and send even more spam?

[JerseyHighlander]

Spammers already know how to exploit this technique and have been doing so for at least 6 years.

They program their bots to find captchas, say the ones to get into Yahoo chat rooms, then copy the captcha image and repost it on their porn websites. The spammers’ porn websites’ users would in order to get to free porn go and solve the captchas, the spammers then take the answer the porn surfer gave and plug it into the target website and also get a correct answer.

When the spammers have several thousand porn sites simultaneously doing this, captcha technology can be defeated with an over 90% efficiency rate.