|I was asked about this so here is my stance on usage of my photos:|
Drawing or Painting reference:
I generally think that if you see it you can draw/paint it so anyone can use my photos as reference whenever they want. You don't need to show me results or link back, although it would be nice to see.
I know I don't want the photos with humans or houses in them being used by anyone else. I also don't like the rest to be treated as stock but if someone asks directly about using any of them I would most likely agree for it to be used.