Writing a "facebook cover" plugin, what approach should I take?

I am writing a "facebook cover" plugin based on previous work done with avatar core feature. Now I am facing my first issue. Avatar is stored as icon for profile, so in order to get the image getIconURL() can be used.

I can not store a second icon for profile, I was considering store cover as an annotation on profile, but now I don't now how to get the actual image URL. Tidypics deals with this creating another entity, should I consider that option? there is a easy way to get image url from filestore?