Pretty fascinating attack on a Time.com poll last spring.  Also includes some hacks against reCaptcha (now a Google company).

Captcha was originally invented at CMU. But, most captchas are eventually defeatable. In response...

Quoted: Microsoft researchers have developed an alternative captcha that asks Internet users to view nine images of household pets and then select just the cats or the dogs

Actually, a new way to make you work for free...

Quoted: reCAPTCHA is more than a CAPTCHA, it also helps to digitize old books.

CAPTCHA for the grammar curmudgeon

Michael Arrington blogged about Akisment filtering out 15,000 SPAM comments per day (!) on their site.

I'm wondering why CAPTCHA is not a better solution.

a) It doesn't require a server-to-server call to validate the comment.
b) Is more reliable as a "real-human" filter.

Can Akismet really stop someone determined to post "spam" on his site by hand, anyway? Spam is in the eye of the beholder. I don't know what Akismet's algorithm is, but it seems to be it's a huge scale issue to have all blogs use a centralized service to perform this function.

Akismet is tailored for Wordpress comment spam, but can also be used for other forms on online posting. There's a developer API here:

http://akismet.com/development/

Kitten CAPTCHA, the next level.

Quoted: Asirra is a human interactive proof that asks users to identify photos of cats and dogs. It's powered by over two million photos from our unique partnership with Petfinder.com. Protect your web site with Asirra — free!