For example, below is the "oldest" family photo in my collection. I have been told that this is William Collins Purdy II and Susan Marie Best. It was probably taken in Staunton, IL, but I don't know when. She died in 1910 and he died in 1912, so the photo was definitely taken by 1910. They both look pretty old, so I'm guessing the photo was taken between 1900 and 1910.
My father looks a lot like WCP2 in the eyes!
More soon. Happy hunting!