custom or virtual tag "has artwork?" possible?

[Space Octopus]

I couldn't seem to find any answer about this, sorry if I missed it. I did look.
I know there's a way to have it show me all my music that contains no album artwork, but I really want it to just show me everything that actually has album artwork and I can't figure out how to do this. I hoped I could create a custom or virtual tag, but I'm not sure what the field is called specifically, or what I would need it to return in order to make this work.  Any help would be appreciated.

[redwing]

Open Tools> Album Artwork Manager and show "no artwork" files.
Select all> Add them to a new playlist.
Create an auto-playlist with a rule <Playlist> <is not> <the one you just created>.
Now you can assign a custom tag value to all those tracks that has artwork.