The Report showed a thumbnail AND 'How many times used' (as well as size info)

You can safely delete '0' use right from the report, since there are not places where a missing image appears.


In Calibre. Use the
Unpack tool and then navigat to the images (folder) and use the explore View menu to show Large Images (thumbnails)
USE CARE, this is not the place for Novices to edit (depends on what else needs to be changed). Safest is to Abort (cancel) after peeking as rebuild puts the changes into the old spot in the library