I can't be sure, but what probably happened is that, the user who posted it has closed their account with the picture-sharing site where it was stored.
When a picture is posted on the forum, the picture itself isn't stored on the forum - it's stored on an outside picture-sharing site, and it's linked to the forum so that the link opens automatically. But if the link is broken, then the picture can't open. So it really can't be "fixed," unless the owner of the picture re-posts it.
I think...