The following sources provided photographs at no cost. (Some sites may also have links to copyrighted material that must be licensed for a fee.)
- Gender Spectrum Photos. https://genderspectrum.vice.com/
- Morgue File. https://morguefile.com/
- Negative Space. https://negativespace.co/
- New Old Stock. https://nos.twnsnd.co/
- Pexels. https://www.pexels.com/
- picjumbo: https://picjumbo.com/
- Pixabay. https://pixabay.com/
- Unsplash. https://unsplash.com/images
- Wikimedia Commons. https://commons.wikimedia.org/wiki/Main_Page
- Wikipedia. https://www.wikipedia.org/