if you open windows explorer and goto organize>folder and search options* and then the view tab, untick the option hide protected operating system files. now browse to the folder and you should see old images that you'll want to delete. they are most likely remnants left behind by the evil that is windows media player.(*exact terminology to find these options may depend on your windows version)
open foobar2k and it's still showing the old art ? how the hell does it even know what the old art looked like ?