* - Photos by Smallbones (Own work) - [Public Domain] via Wikimedia Commons.
** - Photos by Jerrye & Roy Klotz, MD (Own work) - [CC BY-SA 4.0] via Wikimedia Commons.
*** - Photos by Shuvaev (Own work) - [CC BY-SA 3.0] via Wikimedia Commons.
**** - Photographer: William Edmund Barrett. This image is available from the United States Library of Congress's Prints and Photographs division.