U.S. National Library of Medicine Digital Collections: http://resource.nlm.nih.gov/101440841
Images, diagrams and other visual artistic works should be cited just as any other type of work. If you use an image you did not create, you must provide a citation. Image citations should include the following information at a minimum:
Try to find as much information as possible when citing an image. For more on citations, check out this guide.
Public Health Service Tumor Clinic, Marine Hospital, Baltimore, 1950. National Cancer Institute:https://visualsonline.cancer.gov/details.cfm?imageid=1912