I was going to say something about re-sizing photo files -- how it's done in your computer, not on the web - but Cpt. THun beat me to it. Another way around those large files is to use a photo-sharing site (Photobucket, etc). They accept any size file and link to your post with just a line or so of text. Yes, if the photo site goes down your Forum post would lose the photos, but that's a minor concern if you ask me. It's happened once or twice to me in the past five years, and then the missing stuff came back soon anyway.
A plus is that the entire post loads faster.