Or these forums could have a proper auto image resize. These forums are vbulletin. The resources for this are readily available.

Just saying.

I only assumed these forums had this feature already, like most do. I was proven wrong though. Oh well.

EDIT:

It would be a good idea to implement this. Now that I know that the forums don't auto resize images, I personally won't post any oversized images, but some stupid person could come and post a ridiculously large image that would cause people to have to scroll down endlessly until an admin/moderator was here to delete it.