You know, Midgar and NobodyImportant, you could make a smaller version of your screenshots to work as thumbnails.
Sure, SMF resizes the picture dimensions but it can't do anything about the file size. I for one don't particularly enjoy downloading 250 - 600KB 640x480 pictures that would look exactly the same, but would be less than 100KB if you resized them to 640x480.
Please, use your head. Not everyone is on a broadband, and even if they were, there's still no need whatsoever to post fullsized desktops as is.