All my photos in this blog, my Russian blog, Picasa or Flikr are OK to use as an artist reference (for paintings, sketches, drawings). I'm not greedy (well not too greedy, I hope). I would love to see what you do with them but of course it's not mandatory. I normally take only low resolution pictures because they are good enough as reference for my artwork and I can take really a lot of them.
There is a good reference library at
but you have to be a member (its free) to save images.
I can't remember where I took this. Must be in a castle in England.