One of the better means of dating a photo is to identify the photographer. Usually the name (or more correctly the Photographer's Mark) is on the front bottom or back of the mount - the cardboard backing that the photograph is attached to. However, they can be surprisingly hidden - written or embossed on the photo itself or, as one that I saw, in the photograph disguised as a tiny shield.
The photographer's mark usually gives the name of the photographer and the community he or she worked in. The problem is that it is usually difficult to get any further than that to, for example, a date. This site, divided into countries and perhaps regions, will direct you to the books and websites that contain what indexes there are.
But first a word of warning. A remarkable feature of early photographs is that they travelled. They leapt across oceans and continents. If you find an old photo done by a photographer in Brighton, do not assume that it is Brighton, Ontario just because your great grandmother lived in Ontario when she set up the photo album. Consider Brighton, England. If it had been Brighton, Ontario, it most likely would have said "Brighton, Ont" or "Brighton, C.W." Here is a list of regional short forms as are found on photographs.
And here is the index that (we all hope) contains the information you are looking for. Good hunting!
This is an on-going work, and it is not perfect. If you can correct an error or, best of all, add another link, please e-mail me at firstname.lastname@example.org
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