Alternative - save the huge image to your computer, reduce it, upload it to your own storage site. Link to it from there. Of course, a lot of folks don't have such a place, but (as much as I hate to encourage it) ImageShack is one free option.

Some original photo owners get a little upset if they find someone hosting their images on another site, even if just to use it for illustrative purposes (copyright laws and all that). Others apparently have some type of web statistics monitoring that somehow disables the display of the image when linked to on other sites (I've seen that here a few times, often just minutes after the image was first cross-linked).

But, I agree on the huge-ass photo thing throwing the width of the forum off, causing the words to run off the end of the monitor. Huge-ass URLs annoy me for the same reason, especially since they show up on my favorite page - the active topics page. Fortunately, there's a way to avoid that one. Unfortunately, most folks aren't aware of how to use it.

ETA: And, no, I'm not still running 640x480 resolution. I've joined the modern era and have a 1920x1200 screen.