Would be nice to add an option to change the picture in the now playing from album to artist.
Or maybe I missed it?
There are buttons, when it's possible to navigate through multiple pictures.
But as far as I know, there's no way to change the picture shown by default.
Just as Sven wrote, you can browse through all available images. You cannot force a specific type to be set (like other or leaflet) and there's currently no plans for implementing it.