By exposing photosensitive paper soaked in iron salts to light, Hippolyte Bayard created some of the first direct positive prints — beautiful impressions of ferns and lace laid. Sadly, Sir John Herschel invented the Cyanotype the same year, stealing yet another photography milestone from the unlucky Bayard.
Many museums are making selections of their archive of images of art available without copyright to the public, under "Open Access" or "Open Content" policies. These images are relinquished by the museum into the public domain, and are available free of charge for any use, commercial or non-commercial. More About Institutional Open Content