There is a 3rd party plugin that can check for missing artwork references and clean things up, it does this for more then just MP-TVSeries as well, so you could check it out. It is great for those shows that are 'ended' that you deleted from MP-TVSeries database, but the artwork remains.
MPEI -> MPCleaner
It handles MyVideos, Music, Youtube.FM, Moving-Pictures, and MP-TVSeries.