Though not required of public domain images, if you want to credit the library as the source, please use the following statement: "From the San Francisco History Center, San Francisco Public Library" and provide a link back to the item on our Digital Collections site.
San Francisco Society for the Prevention of Cruelty to Animals Records (SFH 75). Box 35; Folder: Panama-Pacific International Exposition (PPIE). Written on back: "Illustrating the manner of removing horses from excavations in an exhibit of the San Francisco Society for the Prevention of Cruelty to Animals at the Panama Pacific International Exposition 1915 in a building erected and maintained by the Society visited by over 200,000 people during 10 months of the Exposition. SF SPCA."