Old family photos are one of my favorite genealogical finds. You might have an image of the whole family, an outdoor scene, or an image of a single child. There might be three photos of a family member at the different ages or only one photo as a child. There is nothing like discovering what your great-great-grandmother looked like (even at age 4)!
Of course, often times you're not lucky enough to find these photos in your attic. So how do you start? Check ebay for photos from areas where your family might have lived. Contact your family and the local historical societies. Check out findagrave.com to see if a researcher has linked their photos to a gravesite... and hope. Good luck! These are incredible finds.