Dating photographs can be difficult. If you have an idea of when a photograph was taken, indicate how you arrived at that date.
Was it because the photograph was in an album and other items on the same page had dates written on them or were able to be dated easily based on events in the photographs?
Was it because someone wrote the date on the photograph? Do you know whose handwriting that was?
If you are using a printed date on the photograph from the facility that printed the photograph, remember that date is the date of printing–not when it was taken.
If the date can be estimated by physical items in the photograph (ie.a car), indicate how you determined the date of that physical item.
If another relative tells you the date of the photograph, indicate who that was.
If someone gave you a time frame for when the photograph was taken, indicate who gave you this time frame and what they based it on.
Just don’t write a date for the photo without documenting where that date came from. That’s how speculation becomes fact.