Lack of free artwork for amateur Visual Novels?

The idea to make a Visual Novel got stuck in my head recently. Searching around led me to Ren’Py – a free (and open source!) game engine designed for such purposes. Documentation is … not what I expected it to be, but it’s passable. My current problem is artwork. For now, I just need some decent placeholder art to use while I learn Ren’Py, but I can’t find anything!