The filesystem is doing the right thing here by accurately storing the original point in time when the photo was taken (or at least it was before you shifted it

The filesystem is doing the right thing here by accurately storing the original point in time when the photo was taken (or at least it was before you shifted it). If two files were modified simultaneously then they should have the same mod times, even if the changes occurred on opposite sides of the planet. The problem is all in the presentation layer; you want your file explorer (or 'ls') to display the times in their original timezone, not the timezone you're currently in. There is an EXIF tag for the time zone offset but support for it appears to be limited. The original timezone could be inferred from the EXIF location data, however, if you have that enabled.