Something I didn't realize about those Captcha things on forms

Maybe I'm late in realizing this, but those "Captcha" spam catchers are
actually doing something useful! I had no idea and always complained that
they're getting so hard to read these days.

They are being used to digitize words in books that have been scanned.
Scanning text, especially old fonts or microfilm that has been distorted, is
quite difficult for a computer to get right without assistance from humans.
For us, we can usually quickly detect a word in the jumble of extra pixels.
But who would want that job?? You might as well sit down and type out each
book by hand if you have to correct half the words that the computer scanner
messed up.

Enter the reCaptcha system. When you're given two pairs of words to
decipher, these can come directly from the scan of text that the computer
couldn't recognize. You give the answer and the computer now knows what
that word is. Obviously with a lot of people answering the same word the
computer can assume that's the right answer. But how does it know you gave
the right answer for a brand new word? That's why they are in pairs. The
first word is one the computer has already verified by asking many people.
If you get that one right you "pass". The second word is under
investigation still, when it becomes verified it gets used as the first
word.

Pretty neat. This page has all the information:
http://recaptcha.net/learnmore.html

You can even set up your own captcha to hide your email address:

i...@slidesinaflash.com