My GMail inbox has been experiencing hell the past few days because of forwarded comment spam from my WordPress installation. Akismet has filtered a lot of spam but the culprits have become more cunning, bypassing the plugin's functionality, sending dozens of moderation notices into my mailbox each day. I wanted to install a new anti-spam plugin. Something that would prevent the spammer from touching the WordPress database.
I just found the right solution with Math Comment Spam Protection plugin, which I bet has the same function as those image verifying plugins.