No kidding? It's probably because imageshack has a higher file size limitation and it takes some users' dial-up connections a lot longer to load the pages with imageshack pix on them. They have a 1MB limit for their free service for each picture. Makes sense, no? You can try photobucket, but they have more restrictive file size limits (250k, I think). I use them for my sig and a few pics here and there. You can also start up a simple site on geocities or something, and have those guys host your files for you. I'm not sure about their limitations, but I do think that they require you to do something with your site now and again or they shut it down due to inactivity. That's the downside about being free. Someone on the Graphix forum mentioned something about http://www.bravenet.com/
being the best free webhost. Don't know from experience, but it couldn't hurt to check out.
Edit: I just thought of something. You can convert your JPG into a GIF to save space, and photobucket will have no problem hosting a 640x480 pic for you. They won't even shrink it, because I doubt you'll exceed 200k with a 640x480 GIF. There's a large drop in quality (only 256 colors), but we'll still be able to make out your cars without a problem.