When should citation information in captions be separated by commas instead of semicolons?

If you provide full bibliographic details in a caption, convert the periods normally used after the elements of a works-cited-list entry into semicolons:

Fig. 1. Vincent van Gogh; The Olive Trees; 1889; Museum of Modern Art, 2001; postcard.

Otherwise, use commas:

Fig. 5. Mary Cassatt, Mother and Child, Wichita Art Museum.