What information (either provided by a user or taken from sensor readings) would be required to determine the geographic area encompassed by a photograph? It seems like the area visible from a photograph would be a rectangle projected onto the surface of the Earth, but I'm unsure what information you'd need to figure out exactly what area a picture encompasses.
It seems clear that you would at least need the location, height, and orientation of the camera (but maybe I'm wrong about that?). There's probably also some information needed about the focal length, but I'm rapidly getting out of my depth here (pun regretfully intended).
As an alternative, suppose that you could get the user to geotag
n points in the picture -- how many points would need to be tagged to compute the geographic bounds of the image?
The use case is that I would like to be able to present various statistics to a user about the area depicted in a photograph; ideally the user wouldn't have to do too much (e.g., if this were done from within a smartphone maybe all necessary information would be available from the phone's sensors), but if that's not possible it's okay to ask the user for necessary information.
Apologies in advance if this is too vague or posted in the wrong area; I'm happy to move it or add clarifying details as necessary.