Board Thread:Support Requests - Getting Technical/@comment-23990955-20140111030619/@comment-303594-20140111122322

A direct link is designed not to be substituted when a new revision is uploaded. This is because the file's revision history always retains these direct links, so that the file can be reverted to an old version or the old version saved and uploaded elsewhere if necessary.

I'd recommend you not use direct links. Wikicode formatting means you can do a lot more with a wikilink to the file. It also means that a link to the file page is there, allowing users to check the copyright information, and the revision history were the image to be vandalised. Also, using wikilinks means you avoid this problem, which is one of the reasons that file revisions were invented in the first place.