I think if you find a thread with vanished images it would be quite old.
If you do, it is a good idea to flag it up to the original poster and ask them to replace the image if at all possible - or to tell one of our lovely moderators who might be able to chase up the original poster if you can't.
We have been making a concerted effort to encourage folk to post images directly to the board for some time. It really is a complete pain when images vanish.