Would be nice to add an option to change the picture in the now playing from album to artist.
Or maybe I missed it?
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.
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.