For example, the following image is 2756 x 2067 pixels, and has a file size of 446.18KB:
http://www.pressrelations.de/presseservice_material/pressemitteilungen/pics/454593_20116150436342593.jpgAfter adding TinySRC to the URL we get an image that is 800 x 600 pixels and 65.4KB:
http://i.tinysrc.mobi/800/600/http:/www.pressrelations.de/presseservice_material/pressemitteilungen/pics/454593_20116150436342593.jpgSo what the reader of the EB forums downloads is the smaller 65.4KB file, but you can always add a link back to the larger image for those that want to see more detail (and can handle the larger downloads).
You can also resize it smaller again (images don't always have to to 800 x 600, here I have resized an image to 320 x 240):
(click the image to see the full sized version)
PS. I know that I have been pushing TinySRC a bit, but I should say that I have no affiliation with them, I just like using their service.
Update: It looks like TinySRC is no longer offering this service anymore
Edited by Splat, 10 April 2013 - 02:53 AM.