Patrick Altoft spotted Google testing a new form of search refinements named “top references.”
Patrick explains the refinement filters you to search through all the existing search results for a specific keyword that show any pages referencing or sourcing that image. Patrick added, “the interesting part of this feature is that unlike other filters the original search query in the search box doesn’t change.”
I personally cannot replicate this myself.
Here is one of the few pictures Patrick shared:
SEOwizz also posted a screenshot of this on his blog.