Irritation, thy name is comment spam

I certain web app I manage that has several thousand users has been really inundated with comment spam over the past 60 hours. I mean, like HUNDREDS of crap messages. It's freakin' ridiculous. I never wanted to have to enforce CAPTCHAs, but it looks like I'm going to have to.

Oh well, building the thing in GDI+ is going to be half the fun.