In the MediaViewer it's made really easy to re-use files from the wiki either on-wiki or using a deep link. It is however not clear what the license is for the file that someone can re-use. To get to know this, a user needs to click some more and look it up by clicking "License information" or on "Learn more on Wikimedia Commons" (which is blocked by the pop-up with the links).
As a re-user, I should be made aware of the license a file has that I want to reuse, so that I can be reasonably informed about the license status of the media file that I'm about to re-use.
A possible solution I see that may be usable, is to provide a title tag with a short license in the field with label "Use this file on another website". For in-wiki links, I think this issue is less pressing, because there's semi-direct access to the file page (see bug 56587).