Often when we look at old family photographs, we develop a kind of tunnel vision. We look at the faces and tend to ignore everything else. Take another look. This time grab a magnifying glass and look closely at the background, searching for clues. Check out family heirlooms, things hanging on walls, clothing, house numbers, cars, or whatever else you see in the picture. Write down what you see. You may find clues that can help put a date on undated photographs. Plus, the background details can add interest to your family history.
-Taken from ancestry.com