If I choose "Cache Last FM album art" and "Cache in music file directory", teacup will save .png files in each music directory, the file name being the album title. This works ok for the teacup widget, but it won't work for the android stock music player: it seems this requires album art files named "AlbumArt.jpg" or "folder.jpg".
Indeed if I rename one of the files created by teacup into "AlbumArt.jpg", the stock music player will display the album art correctly (even if it's a .png file actually).
Please add an option to have album art files automatically named "AlbumArt.jpg" (or maybe this should be the automatic behaviour when the user chooses "Cache in music file directory").
(tested on Android 4.2.2)