Usually Spammers don’t have enough time to manually spam a blog, so they hire robot to do the nasty job. And to prevent them, we use tools like Akismet or Spama Karma.
They effectively block spams, but at the same time they kill good comments as well. Ofcource, you can verify the spambox before hitting the delete button, but sometimes it becomes nearly impossible to verifying each one of them.
They only way to kill these robotic spams is to install Captcha (Captcha is an acronym for Completely Automated Public Turing test to tell Computers and Humans Apart).
While there are tons of Wordpress Plugin which does the job, I use only Peter’s Custom Anti-Spam plugin because its neat and high customizable.
Installation:
Installation is fairly simple, just download the plugin, upload it inside your plugin directory and then activate the plugin through your Wordpress Admin Panel.
This will automatically insert a captcha above your comments form, but if you want to manually insert the captcha code in your template or change the configuration, you’ll need to edit custom_anti_spam.php. Don’t worry, it isn’t that hard, you’ll find all the details with the file itself.
Peter’s Custom Anti-Spam Plugin

wrote, on November 13th, 2006
very stylish and trendy.
wrote, on November 13th, 2006
Good. I do not have my blog that popular yet, and I believe once that happens, I will start to get hit by spam. Then I think, I will have to go for Captcha.
wrote, on November 13th, 2006
You just made your site inaccessible !!!
wrote, on November 13th, 2006
Thanx for that tip and the plugin dude. I implemented that in the blog already
wrote, on November 13th, 2006
@Ajay - i am unable to understand what you want to say. R u with or against using captcha. Please clear, because you know these things better.
wrote, on November 13th, 2006
And, you may want to take a look at http://sam.zoy.org/pwntcha/
wrote, on November 13th, 2006
Ajay: Atleast, its better than Akismet !!
wrote, on November 14th, 2006
Ajay: Nice Find, but not all spammers use these captcha decoders. Even If they do, I have Akismet working in the backend, just I case any spammer manages to get through, I’ll manually filter them