Category:Files with unknown copyright status has items stretching all the way back to 2006, in violation of the Resolution:Licensing policy. A quick suggestion would be, to propose deletion for all files before 2010, and to give a month's notice in advance to uploaders of such files, so they could have a chance to give proper copyright licenses to their files and possibly hold off deletion.
Topic on Project:Village Pump
Before deleting, we could go through them. For instance, the first in the list is a simple screenshot that is not violating any copyrights:
Perhaps it could be tagged as {{MediaWiki screenshot}} but more likely it may still end up deleted from Commons for being out of use on any particular wiki page.
We've had a number of discussions on the topic, please search a bit.
I don't doubt you had numerous discussions on this topic, but at the moment I could not find much. Project:Fair use policy and Project:Image policy were the two closest relevant discussion pages I could find, and I've tried to reignite discussion on the page about fair use here to make it, well, an actual policy.
I started working on tagging them awhile ago, and my plan was to
- Tag all the files I could find
- Get a bot magician to do a report listening them by their uploader
- Update the ones from users where they have made the appropriate licensing comments (TimS and Brion come to mind)
- Start a discussion
- Notify the others with a deadline agreed in the discussion
- Work on deleting the problematic ones
- Try and get stuff moved to commons where possible.