For APA, 7th edition:
Artist Lastname, Firstinitial. (Year of release). Title of artwork [medium]. Name of owning museum, Location City, State, Country. URL of page on which the image appears.
Artist Lastname, Firstname. Title of work. Date of creation. Owning Institution/Gallery/Museum, Location City. Name of Website, URL of page on which the image appears.
These images are publicly available or have limited restrictions. Remember that public domain is always "to the best of our knowledge" and use images according to the restrictions described by each hosting site.