Ultimately people buy music, so the end product is music not image.
I see image as another medium which can be added (and sometimes detract) the experience of a band\music.
Bands can and do use other mediums too. For example, a band may spread rumors about themselves or act in a particualr way to fans and media. This is too affect how the listener percieves the music.
In the end it's all an artform.