Despite the forums attempting to require a human element to register by way of image based confirmation code, it would appear that either some spam-bot exists that will read the code, or someone is sitting around registered to boards all day long so they can later feed the URLs to a spam-bot. I'm inclined to believe it is the latter, due to the significant delay between registration and the first spam post.

In an attempt to help curb this problem, I've enabled account activation for new forum accounts. Basically, your account is disabled until you activate it, which requires a valid email address. As always, I'll continue to watch the boards and ban IPs that post spam.