Files can be found based on their 'depicts' statements using the haswbstatement: search keyword.
A normal user won't know the property id for 'depicts', or the item ids for any of the items that might be depicted, so we need a UI where they can choose these easily. Probably will be the same as the UI for entered depicts data for a file (possibly based on or using wikidata code).
Don't have designs yet, but that probably isn't a blocker.
The interface for Crotos (http://zone47.com/crotos/ ) suggests a number of good ways to do this:
*first as someone searches in the search bar, it suggests what properties/statements you might be wanting to interact with based on the frequency within the term
*As you start to get first results, you can browse some core metadata (including creator and depicts) in the down carrot drop menu which become additional facets for interacting with search results (and get displayed near the search bar as check box components).
Additionally, the Nirzar concept from the offsite, also included a number of other facets that might be of use to power users -- including categories, pageviews, uploaders, templates, license, etc.
Commons MediaSearch https://commons.wikimedia.org/wiki/Special:MediaSearch?type=image uses 'depicts' for searching (among other things) so I think we can consider this to have been implemented. Closing