Well, I can't really understand the page scripting for the image, so that method of investigation is out for me. The image does, however, appear to only link to imagefrog, which is considered clean. I did see an active script for fastclick, an ad server that has been linked to malware in the past, on the imagefrog page. Fastclick currently has a clean bill of health from both macaffee and google safe browsing, though it has a poor rating with Web Of Trust - which may explain your balking browser, Russ.
I don't think the image is, or directly links to malware.
This does appear to be a bogus warning not originating from google. You would do well to take extra precautions. As I said before, you may already be infected.
NEVERMIND: I somehow forgot the adbutler part of the warning...
NEVERMIND THE NEVERMIND: This could still be a bogus warning. Here is the Google Safe Browsing diagnostics page for servedbyadbutler
As you can see, there is no problem with this site on google.
I did find that servedbyadbutler has a poor rating on Web Of Trust. Perhaps google uses their ratings in addition to their own?
After looking around a bit, I can't find anything to suggest google uses WOT ratings in their software. Given that lack and the lack of any negative info. from google, I continue to suspect yours was a bogus warning.Here's an interesting article
relating to this topic. Though it's slanted toward websites unfairly branded by google, it does describe how things work, and how a site might become a victim of malware, despite its best efforts to prevent it.