While searching the name of a photographer in late 1800's Cincinnati, the web site Slices of Time appeared in the list of Google results. This site has a lot of identified and unidentified photos of people from all over the country. There are even some from European countries.
Conrad Caballero, the site's owner, has organized his collection of photos in an easy to locate manner. Buttons on the home page are designated for Photographer, Name, Location, Schools, and Unnamed which will help you in your search for pictures. There are also buttons for his family name index and a Links page containing various links for other photograph and genealogy related sites.
Pages linked to the photo related buttons are also organized in alphabetical order and easy to read. Be sure to click on the red "Please Read" link located on the very bottom of the home page. This will tell you Mr. Caballero's requirements for obtaining a picture. He does not give his photos to collectors so you must have a legitimate connection to the person or persons in the photograph. He does ask for a $10.00 payment which covers his costs. Copies of photographs that have been reunited with their family are kept on the website and are available for a $5.00 donation.
I hope you visit Slices of Time and are lucky in your pursuit of your ancestors' photographs!