By default the 'show now playing artwork' option in the left panel displays the art for the PLAYING TRACK, not for the highlighted track.
However, if you click the pane's header (which says 'playing track'), it changes to 'selected tracks' and will behave as you wish.
This tip might also help you:
· alt+e to bring up the tag manager
· select the 'files with missing artwork' option
· open a new tab. Your library loads. Notice that all the files with missing artwork have a blue exlcamation mark next to them.
MB is showing you the files that don't have embedded or linked artwork.
· you can close the first tag manager tab - the tracks in the other view will still remain flagged
There are a couple of confusing things about this flag though, because MB tries it's best to show something rather than nothing:
If a 'folder.jpg' file exists in the music's folder, MB will display that artwork when playing the file, even though it's also
flagging the file as having none. Similarly, MB could display some cached image too, especially likely if you've had the
automatic download option on.
Lastly, it's quite difficult to refresh those blue exclamation marks; the refresh button doesn't work.
You have to switch away from the view and switch back to it. Eg. click a playlist and then click back to the library.
This gets rid of all of them though, so if you've still got more files without artwork to deal with, you'll need to alt+e again.