I using a couple of methods to assign the artwork to my music files. The source images ranges from really small ones e.g. 100px X 100px to bigger ones like 500px (all jpegs). Somehow, they don't always appear (e.g. on my walkman phone or my wife's ipod), but they do appear on my PC media player.
I'm wondering is it due to the size, aspect ratio or other reasons.