If you, like me, are in e-commerce, one of our main concern is “public-domain” when using work of art images. ALL of the paintings by the old Renaissance Masters are in the public domain; however, if you are using a photo of a painting, that photo may not be in public domain, even if it is in the internet, and sometimes those photos are protected by a copyright.
Thankfully, in the beginning of this year the Metropolitan Museum of art made its images freely available through New Open Access policy, making our lives a little easier, here is about the policy, and how to obtain those images: Images of Artworks in the Public Domain