This morning I woke up extraordinarily early and discovered that Allan was IMing me. So, knowing I had to leave for work in just a short while, I IMed him back, and we had a quite rousing conversation about our photos' metadata.
JPEG photos usually contain information stored in the Exif format. Exif can store a great deal of information about the photo, although many cameras improperly add this metadata to the photos they take.
The crux of the issue is that Exif does not allow for storage of the timezone. To complicate matters, when the photo is downloaded to a computer, the computer has to interpret that timestamp and make assumptions based on the timezone the computer is in. Additionally, the camera may move from timezone to timezone, further complicating the interpretation of the timestamp. Finally, legislation regarding Daylight Saving Time changes next year. The end result is that if you leave off the timezone, it's similar to writing a distance without specifying "miles" or "kilometers".
Timestamps are meaningless without an accompanying timezone.
Set your camera to UTC, the timezone formerly known as Greenwich Mean Time. It always marches on consistently, never minding timezones, legislation, or oddball locations like Detroit which is about 32 minutes behind Central Standard Time. UTC doesn't change!
This is, of course, a pie-in-the-sky solution, the kind I seem to luck and latch upon while others are forced by outside circumstances to stumble along, short of my proposed perfection.
After talking for some time about photo dates and times, Allan and I signed off. Note that my reply is about 30 seconds after his goodbye.
(02:30:47 PDT) Allan Tokuda: cool. I'm off to bed
(04:31:11 CDT) Kurt McKee: i'm going to get ready for work. [JPEG]: Joint Photographic Experts Group [Exif]: Exchangeable image file format [UTC]: Coordinated Universal Time [PDT]: Pacific Daylight Time *[CDT]: Central Daylight Time