Now that a large percentage of media files on Commons have license data in their structured data, we should add a drop down to Special:MediaSearch allowing the user to filter by license:
- All licenses
- Creative Commons Attribution
- Creative Commons Attribution-Share Alike
- Public domain
The CC0 option, for example, would filter for haswbstatement:P275=Q6938433. Note that some of these options cover multiple license items in Wikidata.