I too am currently stumped about how to deal with TV cover art. I currently don't know where MC is pulling the art files or screen-grabs. Sometimes I have luck browsing by "Folder" in Theater View and just using my TV series path (I think it is using folder.jpg), other times browsing by Series, Season, and then sorting by episode works better. They produce different cover art results at all hierarchies.
Do I need to use the TVSeries(GetInfo) field in order to properly use TV cover art? What exactly does this field contain?
Could someone provide a straight-forward explanation of how to apply episode, season, and series cover art?