Kendo - 7:16 am on May 23, 2012 (gmt 0)
especially as so many CAPTCHAs are becoming unreadable
Yes, Captcha has become unreadable to us humans, but spamming software can still read it. So it has become illegible yet we are still losing the battle. Third party Captcha services have advanced to the point of being useless. On one site today I had to refresh 20 times before I could read the Captcha, and it's the same one that I see on most sites.
So forget Captcha and kill spam the easy way:
1. use referrer checking on your join and contact pages
2. use a simple question/answer instead of Captcha
Referrer checking should do the job on it's own because when anything lands on your page from a direct link the refering link won't be from your site, in which case you can redirect. I use this method on several sites and have had no spam since.