The following are websites helpful in dating pictures

• Photographers of the 19th Century
• Photographers in Chicago from 1847-1900
• Early Michigan photographers
• Directory of Minnesota Photographers ​
• List of early St. Louis Photographers
• List of Fargo, ND Photographers
• Oregon Photographers: 1852- 1917
• List of Lancaster County, PA photographers
• List of 19th Century Photographers in Ayrshire, Scotland
• History of fashion 1840-1900 ​