Luigi Cavalieri

RedBrick is able to block most of the automated spam comments a WordPress blog receives daily.
It is based upon a score system that ensures spam comments are blocked as soon as possible, so as to minimise the number of checks each comment must go through. When in doubt, RedBrick always holds the comment in the moderation queue. Comments identified as spam, however, never reach the database.
As a last resource in discerning the kind of comment under examination, RedBrick takes account also of the comment author’s history.
The plugin is designed to work on low-to-medium traffic blogs.

RedBrick

Simple anti-spam plugin for WordPress blogs.

Peter

Stop a lot of spambots from polluting your site by making visitors identify a random word displayed as an image before commenting and optionally before registering. You can customize the pool of words to display.
<h4>Features</h4>
<ul>
<li>
Toggle whether registered users need to enter the word
</li>
<li>
Random font display
</li>
<li>
No cookies required
</li>
<li>
No JavaScript required
</li>
<li>
Auto-generated audio for visually impaired users
</li>
<li>
Easy-to-read
</li>
<li>
No mapping of words from the code — words are used once or removed after 24 hours
</li>
<li>
Reminder of what was entered if you get the word wrong
</li>
<li>
Selective blocking of trackbacks, pingbacks
</li>
<li>
Easy to translate
</li>
<li>
Compatible with caching plugins
</li>
</ul>
<h4>Negatives</h4>
<ul>
<li>
Purposely no obscuring techniques so that the anti-spam word is easy to read
</li>
<li>
The more people who use this plugin, the more motivation for spambots to target it
</li>
</ul>
<h4>Requirements</h4>
<ul>
<li>
GD Library and FreeType Library (There’s a diagnostic page to tell you whether you have them installed. If needed, just ask your web host to install them!)
</li>
<li>
WordPress 3.2 or higher
</li>
</ul>
<h4>Translations</h4>
<ul>
<li>ru_RU translation by koc</li>
<li>sk_SK translation by Patrik Žec (PATWIST) of http://patwist.com</li>
</ul>

Peter’s Custom Anti-Spam

Stop a lot of spambots from polluting your site by making visitors identify a custom word displayed as an image before commenting.

RedBrick vs Peter’s Custom Anti-Spam