I've been hunting Pinterest and have accumulated vintage, nature prints great for mixed media artists who collage and create with vintage images. This post's pinboard shows a sample - but not all; so, be sure to click through if you'd like to see the entire board's haul.
My Two Cents
Collage artists and mixed media artists take 1 image, and create 1 artwork - a creative commons approach. As most often, something completely different from the original, vintage image is the result, it also does not lead to mass reproduction of the image. Accept eachother's right to Creative Commons use, but do not abuse.