Filtering by Cover Art

Can anyone suggest how to filter a list by cover art. I have tried everything to no avail

It is not quite clear to me why you mean by

If you want to see the files that have cover art:
%_covers% PRESENT
or the opposite:
%_covers% MISSING
Or what did you have in mind?

I am looking at filtering the list with covers MATCHING a string value, that is the name of the cover art,

you can filter for the type of a cover (front, back, artist, etc.) (%_cover_type%)
You cannot filter for the label.

Thanks. I will work on this to see if it does what I want it to do.