I DESPISE Captcha. What is it?
I wrote a post on this last year (my most popular!) but Blogger has updated their interface, so the visuals on that post are obsolete (updates - the bane of the digital instructor).
Here's how you do it now...
1) Go to your Blogger Dashboard
(upper right of this page, or hit Design when on your own page, then go to Step 2)
2) From menu on the left, choose Settings
3) Choose Posts and Comments
Show word verification, Choose No
5) Be sure to hit Save Settings, on upper right!