I think it would be helpful to write the images and metadata for song tracks to the filesystem, rather than just the server cache.  This way, a custom image for a song (CD Single artwork, etc..) would be permanently stored, much like movie posters and album art is now.   If the song is /Bad Company/10 From 6/Bad Company.mp3 Then write... /Bad Company/10 From 6/Bad Company.jpg /Bad Company/10 From 6/Bad Company.nfo