An interesting article from /. today on defeating Captcha systems. The site referenced in the article lists several Captcha systems that it's program has been able to defeat so far, along with their relative weaknesses.

What may be of interest to ColdFusion developers is a CFX tag, CFX_Captcha has not yet been defeated by the system, and is listed as "A Very Good Captcha" on the PWNtcha site.

It should be noted that the site hasn't been updated in a while, so it is entirely possible that CFX_Captcha has also been defeated. The site author has stated that an update is coming soon.

In the meantime, my personal feeling on Captcha systems is that I don't like them. Although I can appreciate the intent, as a color blind individual, I find many of them difficult to read. I can only imagine the frustration for users with more severe/serious vision issues.