Well, that was anticlimactic.
The webmaster obviously found the graphic and removed it. Bummer. That was quick.
I still will email everyone whose email address is on the site and tell them what I think about their bandwidth theft.
Hometownboy, if you actually feel that there’s a story here, email me and I’ll give you the guy’s URL!
I think you did the right thing by putting up someting harmless that still got the point across. 
Messing with the politician’s reputation by putting up something offensive would have been going too far in my opinion.
Just a thought - as good neighbor sort of gesture, you might want to drop emails to the other sites that he’s stealing bandwidth from and let them know what’s going on. Not everybody pays that much attention to their usage reports and they might not have noticed the transgression.
You might also want to have a gander at the site and see if you notice anything being stolen from anywhere else, just in case he’s switched his stealing for some reason (say, someone else having this conversation). If so, then you could email the other victim and suggest complaining, and if that doesn’t help, go down the mischeif route.
I did. 
Damn, yosemitebabe. Seems like you have to put up with more than your fair share of this nonsense.
quoted for truth
Depending on your server setup, there may be technical means to prevent the hotlinking of images on your site. You may be able to block it completely, show an alternate image on the hotlinker’s page, or possibly even redirect the browser to another site. Google “hotlinking”; there’s lots of info available.