Some time ago Campbell released this video - http://www.youtube.com/watch?v=mRiTfLpRlRU , and later wrote:
You can use OpenGL to draw pretty much anything, graphics - images etc.
Though this isn’t the main goal of py-buttons to draw graphics, its possible.
and it was in response to my question about adding icons to addons. So - anyone maybe knows if it really is possible? I am aware that icons are stored in a single png in Blender, that you can modify when building, but the question is about adding them to addons.