All good answers - show & tell. I inherited a large collection which had been reviewed by many descendants and neighbors for about 15 years before I received it, but about 25% were still unidentified. After scanning all of them, I downloaded a free facial recognition software, which mainly confirmed the ID's of similar faces, especially in group photos. Studying the extended families helped identify gaps to fill. Another skill is learning dress styles and other ways to date a photo. Sometimes the photographer helps narrow era and place. Recognizing family facial characteristics ID'ed a few more. I've uploaded some to a free space page here. Facebook has a hometown page where I occasionally upload an unknown. I also opened a cloud account and have shared the collection with a dozen or so extended relatives, who have in turn uploaded their collections. Ongoing, never-ending project, but one most intrigueing.