The ARTstor Digital Library provides more than one million images with tools for teaching and research. Its collections comprise contributions from outstanding museums, photographers, libraries, scholars, photo archives, and artists and artists' estates from all over the world. The collections encompass a wide variety of subject areas, including art, architecture, music, religion, anthropology, literature, world history, American Studies, Asian Studies, Classical Studies, Medieval Studies, Renaissance Studies, and more.
Just like you would cite any textual source you use in a project or paper, you should give proper attribution for any images and/or videos you include.
The basic information you should always note includes:
See Open Washington's Open Attribution Builder for works in the public domain or with a Creative Commons license.