Reduces spam and troll comments by requiring commenters to answer a question.
When you write a post, enter the question and answer in the "Comment Quiz" meta box. If you leave it blank, the default question will be used. If you enter "noquiz" as the question, that post will not display a quiz.
To manually place the quiz form within you comments section, edit the comments.php file and insert the following: do_action('comment_quiz')
There is a Settings screen if you want to customize things, including setting the default question or customizing the way the quiz displays on the page.
Tips on how to improve questions can be found at http://striderweb.com/nerdaphernalia/features/wp-comment-quiz/
(Please Note: the old "quicktag" method no longer works. If you want to use that method, you should download version 1.0. In 1.1 and above you enter the question in the meta box.)