Chronolocation: putting a time on the picture
Geolocation answers where. The same sun answers when. Once a location is fixed, the shadows in a frame stop being scenery and become a timestamp that no editor can strip out.
The sun is deterministic
Solar position, its azimuth and elevation, is an exact function of latitude, longitude, date and time. That function runs backwards. Measure the sun in the image and you recover the clock that made it.
- Direction of a shadow gives the sun's azimuth, which maps to time of day.
- Length against an object of known height gives the sun's elevation, which constrains the date.
Where it gets hard
You need a vertical reference, reasonably flat ground, and a rough location to begin. Sun elevation is also ambiguous: two dates either side of a solstice share the same angle. Foliage, snow, weather and other dated cues break the tie.
Done carefully, chronolocation corroborates a claimed timeline or collapses it, and pins a loose image to a specific moment. That is the difference between "around then" and "twelve minutes before it happened".