I have seen this in use in another website and it worked great, and know I think we should have it here. A preview button! What it is is a little button that lets you preview what you are about to post before you post it. This would avoid all those problems with images and links that do not work that need to be posted again, and again just to get it to work. The button could go next to the 'ost comment' button, as it would be the most logical place to put it. I don't know if it has been suggested before but I think it is a really good idea and would help everyone.
Darnit, mrtim beat me to it -- it's been suggested a few times here and there, most people opt for the Edit button (which would require more coding!)
Anyway, it doesn't have to be limited to the scope of pictures and links -- spelling errors or forgotten thoughts could be minimized as well. Instead of an option of previewing, people should be forced to go to the Preview page first before posting (i.e. when you click "Post your Reply", it goes directly to the preview page). I guess some people would be impatient and get frustrated everytime it happened, but it'll cutdown on: double posting, spelling errors, etc.
InTheZone's idea is very similar to the one they have on Gamefaqs
Exactly what I was going for. Albeit, the quality of posts on GFAQs sucks -- there's little double posting going on (of course, they have a built in spell checker).
This suggestion is nothing new. Mrtim's link will show you a list of popular suggestions that AG staff is already aware of, including "ost preview".