"Open access is a broad international movement that seeks to grant free and open online access to academic information, such as publications and data. A publication is defined 'open access' when there are no financial, legal or technical barriers to accessing it - that is to say when anyone can read, download, copy, distribute, print, search for and search within the information, or use it in education or in any other way within the legal agreements."
(From the web page "What is Open Access? — Open Access.NL. See more at "https://www.openaccess.nl/en/what-is-open-access")
Open Access materials have no copyright restrictions and should be sought out first when locating third party materials.
Below is a selection of museums that provide open access to portions of their collections. For links to more museums, see the following resources, which include some links to European institutions.
"Open access image libraries – a handy list." Apollo Magazine, February 28, 2020. Retrieved March 4, 2021
"Public Domain Images For Artists." MoMa.co.uk. Retrieved March 4, 2021