All of my photographs are FREE to use as reference for personal and commercial use in drawings and photo-manipulations. And you do not need worry about crediting or linking back to me.
But I do have 2 rules!
1.DO NOT copy/paste my photos and claim them as your own. You MUST change the image in a significant way. Don't just scribble something like your name on my photo and call it good.
2.DO NOT use them in pornographic photo-manipulations.