When using information from another source you must give credit to the original author or you are plagiarizing. You give credit by citing the source. Make sure your citation contains everything you would need to backtrack and find the information again. It is best to pick one citation style and be consistent.
For the class assignment related to the J. Randall Plummer Photography Collection and information on how to cite photographs, see especially the Library of Congress' Guide to Citing Photographs in MLA Format. Similar to citing journal articles and books, images should be cited according to a recognized citation standard such as MLA, Chicago, APA etc.
Below is an example of how to format a citation for a photograph according to the MLA Handbook, 8th edition:
MLA Citation Format
Artist last name, artist first name. Title of the photograph. Date of creation, version/format (photograph), archives, library, or other Institution, Country, State, City. Title of the Website, date published on website, URL or DOI. Day month and year of access.
Evans, Walker. [Barber Shop, Vicksburg]. 1936 and printed 1950s, gelatin silver print photograph, Archives and Special Collections at the Penn State Harrisburg Library, Penn State University Libraries, Middletown, Pennsylvania. Flickr Album for Penn State Harrisburg Archives and Special Collections, J. Randall Plummer Photography Collection, 21 June 2017, https://www.flickr.com/photos/pennstate_harrisburg_archives/ 37097942250/in/album-72157687174320434/. Accessed 11 Nov. 2020.