since pictures are hosted offsite, resizing the actual photo wouldn't be possible
it might be possible to detect width and set a smaller width attribute in the img tag after it loads - but the user will still have to download the huge image.
the programming and overhead involved is likely not worth it. we're better off educating people
It is definitely possible to have forum software resize the image automatically even with a picture that is hosted elsewhere. I do it all the time on other forums that I am a member of. This is the only one that I'm on that doesn't do that. I obviously can't say if it is a feature that is available but I'll seconds Gummi's interest in it. I hate having to get 2 different image files ready when I want to post the same image on multiple sites. It makes me less inclined to post it here.
If you do find a way to make it work, I'd definitely appreciate it but will understand if you can't make it happen as forum software is not all equal.
To clarify - it is NOT possible for the forum software to resize an image that is not hosted by the software.
There are 2 scenarios that you may be experiencing.
1: The software is displaying a smaller sized image automatically, but the file is NOT resized. The client browser still downloads the huge file. This isn't ideal as it creates a bad user experience (although a huge image loaded inline is already a bad experience)
2: the software makes a copy of the file, resizes that copy, and displays the self-hosted resized copy. This is the ideal solution, but involves a lot of tech overhead AND space.
I'm looking into ways to improve photo posting and hosting.