Using CAPTCHAS is a common way to help stop automated Web form submission. However, they're routinely cracked so perhaps there's a better way?
Here's a case in point: Xrumer is a tool commonly used to automate registration a countless numbers of forums, and with the latest version (5.0A) people can also automate registration on sites like Hotmail and Google. Bigshot companies like Google and Microsoft can afford to throw a lot of money at captcha development to make images that are difficult to read with automated software. Nevertheless the latest version of Xrumer reportedly cracks some of the most difficult CAPTCHAs.
Any Internet spammer (who are incidentally akin to spray paint taggers that destroy public property) can buy a copy of Xrumer for about $520 (at botmaster.net) and set it loose registering new accounts and spamming the Internet. Others use Xrumer as a tool against their competition. For example, by spamming the right places with the right kinds of text and links a person can knock their competition out of Google's ranking.
What I'm wondering is why anyone even bothers using image CAPTCHAs anymore? Seems to me that what would be far more difficult to crack are questions and answers. In place of the CAPTCHA you pose a question with a known answer. For example, a simple math problem, environmental questions (what color is the sky on an overcast day?), silly questions (does a dog bark or meow?) or similar.
I gave up on CAPTCHAs quite some time ago and opted for the question method instead. So far, so good.