The VideoLAN Forums

I can add cover art okay, the problem is making it stay. As soon as VLC gets closed, it forgets everything I told it, and the next time it's back to either blank or incorrect cover art.

Pause the playback of your media, then you need to modify at least one of the fields (e.g., Title, Artist, Album) for making the Save Metadata button to appear. Once it's there, you can even cancel the previous edit.
Now you can add a cover and then save it using the Save Metadata button.

Pause / Media Information / Change one of the fields / Save metadata button appears / Add cover art / Save metadata / Close.

I did that, but the problem persists. Next time I played it, it was back to the wrong one.

Exit VLC and delete the whole %APPDATA%\vlc\art folder.

Deleted it, problem persists.