I think it's worth noting for the record that Deb Wythe and the Brooklyn Museum began making public domain images available way before other US museums, and with fewer restrictions. Brooklyn (and to some extent the Met) have been early in moving toward open, free access to all p.d. images.
To do so, Brooklyn has had to mount a huge project to research the copyright status of every work. As Peter Hirtle's chart tells us, determining whether a work is p.d. or not is not always a cut-and-dried thing. That said, the next stage of this process is looming: to make all p.d. images available for all uses--including highly commercial ones--without trying to monetize the process. Deb, the one bone I would pick with you is on the question of how difficult or onerous the paperwork and research are for end-users. The process is out-of-control burdensome, with as many as 3 or 4 different stakeholders all claiming authority to grant or withhold access. In NYC, if one wants to get a permit to do work on one's building, the process is so entangled, and so many people need to be bribed, that it has given rise to a career known as an "expediter." Likewise, museums, publishers, and individual authors are having to hire rights-clearance professionals just to get access to pictures that are freely found everywhere on the Internet. And lastly, the Internet is full of those pictures, but by and large the quality is terrible. The museums who are the stewards of art and who profess to care most about the artworks have taken great care to keep their high-res, large-size, color-corrected scans as unavailable as possible. Instead, the bad ones--the cheap scans from books, the old outdated faded copies--are what the public (and the arts community) has access to. I cannot fathom how this can be said to meet museum mission, or serve art well. In a nutshell: the advent of the Internet changed the game, and museums are now, step by step, coming to terms with that. Regards, Eve Sinaiko NYC