I want to dictate to PLEX what art to use

Actually I found another post that has more information about the filenaming options that Plex will recognize.

Whups, just realized you can’t see that post, as it is in the Plex Pass area. Here’s the info from it regarding art files:

ext = jpg, jpeg, png, tbn

ARTIST POSTERS:
recommended structure: /artist-album/media.mp3:
    artist.<ext>, artist-poster.<ext>, artist-default.<ext>, artist-cover.<ext>, artist-folder.<ext>
also supported structure: /artist/album/media.mp3:
    same as above + 
    poster.<ext>, default.<ext>, cover.<ext>, folder.<ext>


ARTIST BACKGROUND:
recommended structure: /artist-album/media.mp3:
    artist-fanart.<ext>, artist-art.<ext>, artist-background.<ext>, artist-backdrop.<ext>
also supported structure: /artist/album/media.mp3:
    same as above + 
    fanart.<ext>, art.<ext>, background.<ext>, backdrop.<ext>


ALBUM POSTERS:
[album, poster, default, cover, folder].<ext>

ALBUM BACKGROUND:
[fanart, art, background, backdrop].<ext>