Joe Stewart from SecureWorks has put together an effective "eye chart" that sources its graphics from sites that Conficker would block. Click here to test the eye chart. If you can't see one or more of the images, you're either infected, or image loading in your browser has been disabled.
Firefox users can check if image loading has been disabled under Tools/Options and the Content tab. Load Images Automatically should be checked. Internet Explorer users will find it under Tools/Internet Options, then the Advanced tab. Scroll down to Multimedia, and Show Pictures should be checked.
It's a test based on the fact that Conficker blocks legitimate security Web sites. The logos are sourced remotely, so if they can't load, the sites are also likely to be blocked. If you're seeing blocked images, you should check out the CNET guide to removing Conficker--just because the botnet hasn't done much that's demonstrably malicious yet doesn't mean it can't or won't in the future.