I have recently installed the SI Captcha Anti Spam plugin by Mike Challis so I could safely open up the ability for people to comment on this site.
So far so good easy to install and set up and the number of spam events so far is zero (asking for trouble with that statement).
Features as described by the author are as follows
Some of the many features include:
- Configure from Admin panel
- Allows Trackbacks and Pingbacks
- Setting to hide the CAPTCHA from logged in users and or admins
- Setting to show the CAPTCHA on the comment form, registration form, login, or all.
- Valid HTML
- Section 508 and WAI Accessibility Validation.
- I18n language translation support
- (see readme.txt inside the zip file for full instructions)
Captcha Image Support:
- Open-source free PHP CAPTCHA library by www.phpcaptcha.org is included.
- Abstract background with multi colored, angled, and transparent text
- Arched lines through text
- Generates audible CAPTCHA files in WAV format
- Refresh button to reload captcha if you cannot read it
Excellent plugin not a lot else to say.