I want to thank Esther Fuldauer for this plugin.
It has been a long time fighting against SPAM in the comments on my weblog. The first step was moderating them, but when you recive almost 100 spam comments at the same time, it’s difficult to manage all them.
The solution goes through this plugin. This plugin adds a random image in the “Post Comment” page, and you must retype it in the text field below. If they so not match, you cannot post it. It’s easy for a human being, but hard for a robot or bot.
I’m sorry for this inconvenience, but I think you will understand it.
You can find the plugin and the installation instruccions here.