I am not sure if this works with really old family photographs or not (probably not) but it still can be a very useful tool.
How can open source investigators determine when a photograph or video was taken?
Observing the length of shadows visible in an image or clip and employing tools like Suncalc offers one useful method.
But this process of “chronolocation” – determining when a picture was taken rather than just where (which is known as geolocation) – isn’t always feasible. For a start, it has to be daytime and there must be a shadow cast somewhere in the video or image of interest.
If these options aren’t available, looking for other clues in a “source” image that can be cross-referenced with contextual “reference” images or other related information can also help narrow down a date range.
Bellingcat has used such chronolocation techniques to determine when undated photos in a museum archive were taken and to find out when a Czech politician’s son (who claimed to be kidnapped) had been photographed.
Clues to look for in a source image may include:
Buildings (especially their façades)
Construction sites
Storefronts (similar to buildings but might be even more useful as this changes more frequently).
Seasonal indicators such as weather, foliage etc.
Natural landmarks
Clock towers
Public transport stops, bus lines etc.
Graffiti and murals
Banners
Advertisements
Essentially, any aspect of a source image could be of use, provided that it has changed over time. Sometimes clues will be so obvious that it’s possible to immediately figure out the rough date of the source image from one detail alone.
You can read a lot more in an article by Youri van der Weide published in the
bellingcat.com web site at: https://tinyurl.com/bda5vpt3.