Comment 3 for bug 1372000

These are the filenames i've seen:
folder.jpg
.folder.jpg
cover.jpg
album.jpg
albumart.jpg
front.jpg
$artist - $album.jpg

I managed to find this question [0] on askubuntu, which was actually has an answer from James Henstridge :)

Note that it also states what Rhythmbox does:
'From where is artwork fetched?
Rhythmbox uses last.fm to look up artwork. If you have local image files, saved in the same directory as the audio file(s) with the filename "cover", "album", "albumart", ".folder", "folder" or "$artist - $album" Rhythmbox will use them instead of looking up a cover on last.fm. It will also use images extracted from file tags.'

0 - http://askubuntu.com/questions/123612/how-do-i-set-album-artwork