That's interesting. If the iPad has location tracking enabled, it doesn't need cell connection to get close enough for this purpose. Not sure if it has gps or not. I know the Windows location tracking can use known wifi that is in the area to locate the device even if you don't connect to the wifi. I assume the Apple devices have something similar.

Then it's just a matter of comparing the picture time stamp against your location history. Or you might have one of the Nikon cameras that does actually have builtin gps. What model?