Langdon's List of 19th & Early 20th Century Photographers
Langdon's List (Web site)
Barbara R. Langdon
Aiken, SC: Langdon & Langdon
"This site provides information about photographers active in the United States from 1844 to 1950. The information comes from city directories, business and industry directories, classified advertising, tax lists, census, published sources and photographer's marks on the images themselves."