I typically crop, but haven't messed with resizing for the forum.Of course there is a way to do that. You need some kind of photo editing program. I think cell phone can resize also, not sure though since I use photoshop. I size most of my internet/computer images to make 5 inches on the longest side @ 100 dpi.
Forum itself. I can post the same photo here or another forum, but only here are they displayed so large. If nobody else is having the issue it may just be something in my account settings I need to explore.Or are you referring to within the forum itself and photos someone else has uploaded?