Like with books, you may need BROADER terminology to help find relevant images
Instead of Florence Nightingale --> Crimean War AND nurse
Review resource descriptions to ensure they match the time period and content area of your research topic
Example
Stanis, A. [Collector]. (1940). Polish American Women's Political Club - Red Cross Unit, 1940 [Photograph]. Retrieved from https://bentley.umich.edu/research/guides/poles/images/redcross1.jpg.
This would be a good primary source image of to document nursing uniforms of the 1940s, the connection between politics and nurses, or the role of Polish Americans in formulating a nursing identity.
The Digital Public Library of America brings together the riches of America’s libraries, archives, and museums, and makes them freely available to the world.
Online collection of written and spoken words, sound recordings, still and moving images, prints, maps, and sheet music documenting the American experience.
A treasury of online, high-resolution images, including landscapes, parks, environmental images, portraiture, the Mid-Mountain West, and a large collection of World War II photographs.
Contains primary source material from the University of California Libraries, ranging from the 1770s to the 1970s. Powered by the California Digital Library.
The Library of Congress has made digitized versions of collection materials available online since 1994, concentrating on its most rare collections and those unavailable anywhere else.
Search millions of photographs from the LIFE photo archive, stretching from the 1750s to today. Most were never published and are now available for the first time through the joint work of LIFE and Google.
The National Photography Collection is best regarded as a collection of collections, which comprises the Daily Herald Archive, the Royal Photographic Society Collection, and the Kodak Museum Collection, amongst other world-class objects and images. Part of the National Media Museum in Bradford, England, UK.
Digitized items from the New York Public Library, this is a living database with new materials added every day, featuring prints, photographs, maps, manuscripts, streaming video, and more