Last year when I spoke at the High Point Library about preserving old photographs, I mentioned how I had identified some 19th and early 20th-century family photos that weren't labeled.
1. Learn to recognize faces. After looking at many different pictures, I learned to recognize my great-grandfather, his mother, and his uncle, even when they were very young or very old.
2. Compare frames. As I recognized my g-g-g-uncle in one photograph with a white, textured paper frame, I remembered that one of my unidentified pictures had that same kind of textured frame. That connected the person to my uncle, probably from the same sitting for a photographer. After comparing the faces with other pictures, I realized this was his youngest son, but much older than in any of his other pictures.
3. Use genealogical research to fill in other people. In a five-generation photo, I knew everybody except the little boy. I found out that the young lady in the photo only had one son and he was her first child (which would make a family want to pose for a 5-gen photo). A more mysterious photo had my young g-grandfather with a young woman, who looked nothing like my g-grandmother. Paw was an only child, so who could she be? After extensive research, I realized that he grew up in the same household with his aunt - they were one year apart. I concluded that they must have been like brother and sister, and therefore posed for a portrait together.
4. Look for clothing clues. I'm very much an amateur in this area, but Maureen Taylor is an expert. I enjoy reading her blog about how she solves photo mysteries.
5. Use the type of photograph (daguerreotype, tintype, paper, etc.) to narrow down the timeframe when it was taken.
6. Use photographers' marks to further narrow in on the year and possibly the location of the photo.
One of the people who came to my class at the library recently sent me a photographic puzzle, and step no. 6 turned out to be a huge clue. I'll tell you more about it in the coming week.