Guidance directly from the Chicago Manual of Style:
The pattern for image notes is:
#. Firstname Lastname, Title, date, medium, height × width × depth (unit conversion), location, accession number, URL
The pattern for image bibliography entries is:
Lastname, Firstname. Title. Date. Medium, height × width × depth (unit conversion). Location. URL.
Let's say you found a photo of an artwork at a museum's website. Here's a footnote example:
1. David Alfaro Siqueiros, Echo of a Scream, 1937, enamel on wood, 48 x 36 in. (121.9 x 91.4 cm), Museum of Modern Art, New York, object number 633.1939, https://www.moma.org/collection/works/80144.
Here's the same footnote turned into a bibliography entry:
Siqueiros, David Alfaro. Echo of a Scream. 1937. Enamel on wood, 48 x 36 in. (121.9 x 91.4 cm). Museum of Modern Art, New York. Object number 633.1939. https://www.moma.org/collection/works/80144.
You may not always have all of these pieces of information; in that case, omit the pieces you don't have. For example, if the artist is unknown, it's usual to start with the title of artwork.
Museums will usually provide an accession number, which is a unique number assigned to the object within the museum's collection. Use whatever term for this the musuem uses, such as accession number, object number, reference number, and so on.