The Met's collection contains over 375,000 images of art in the public domain; they've made these directly searchable and browseable, there's a Github repo of metadata, integration with the Creative Commons search tool, and extensive collaboration with Wikimedia and GLAM Wiki.
"The Met has again proven itself a leader among the world's great cultural institutions. By opening their vast collection of art and antiquities to be freely available under Creative Commons Zero, they are lighting the way for other institutions to follow," said Katherine Maher, Executive Director of the Wikimedia Foundation. "Wikipedia's hundreds of millions of users from around the globe will now be able to experience The Met's greatest treasures, no matter where they live. This remarkable cultural heritage is now free for anyone to view, share, and use."
Loic Tallon, The Met's Chief Digital Officer, said: "In our digital age, the Museum's audience is not only the 6.7 million people who visited The Met's three locations in New York City this past year, but also the three-billion-plus internet-connected individuals around the world. Adopting the CC0 designation for our images and data is one of the most effective ways the Museum can help audiences gain access to the collection and further its use by educators and students, artists and designers, professionals and hobbyists, as well as creators of all kinds. I am particularly delighted to be launching the Museum's CC0 policy in collaboration with Creative Commons, Artstor, DPLA, Pinterest and the Wikipedia community, and for their support in bringing the Museum's collection to their users."
We've created 20 thematic sets of images to get you started: Masterpiece Paintings, Cats, Monsters and Mythological Creatures, Met-staches, New York City, Impressionism and Post-Impressionism, Winter Wonderland, Vincent van Gogh, The Pre-Raphaelite Style, Self-Portraits, Quilts, Gold, Georges Seurat, Arms and Armor, The Monuments Men at The Met, Faces from the Ancient World, Tiffany Glass, Dress to Impress, Art or Design?, and Dishes.
Public domain art [The Met]
The Met Makes Its Images of Public-Domain Artworks Freely Available through New Open Access Policy
The Met Makes 375,000 Public Domain Images Available