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From my previous question I am using the following ExifTool command to add Exif Date info to some photo.

exiftool -v "-FileModifyDate>AllDates" *

However, since we went back to GMT from BST, if I try use this on a photo which was taken during BST the Exif Dates are now all out by 1 hour. Photos taken after the switch are fine

e.g. after running ExifTool:

Photo taken BST, modified time of 11:00, Exif DateTimeOriginal is 10:00

Photo taken GMT, modified time of 11:00, Exif DateTimeOriginal is 11:00

Is this expected behaviour? Is there an override switch which will force exiftool to honour the exact modified date/time and ignore timezone differences?

EDIT: I'm using the Windows version of ExifTool

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You know, I bumped into something like this a few days ago.

I decided that from here on out, all my cameras will be set to UTC no matter where I am or whether it's daylight savings time.

Then, there won't be any need to figure out what time zone a given timestamp is in, or deal with changing the camera's clock when daylight time starts or ends. (FWIW, I went to make the latter change only to discover that it was still set to the time zone I had put in for a trip months ago. That's what prompted the decision.)

  • This is more and more inconvenient the farther from the prime meridian you are, because if you're off by more than a few hours, the date on the photograph will often be off by a day. For this reason, I do the same thing but using EST (never EDT) as my base. – mattdm Nov 26 '10 at 15:21
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    Date and Time is a common source of problems for software, and the general advise is to store in UTC, and then render to the right timezone. I suppose EXIF doesn't make that easy. – Calyth Jan 10 '18 at 13:42
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On Linux, you can set the TZ environment variable to GMT (or whatever), and that will be honored by every program. Either export TZ=GMT in the shell before you run the commands, or else prefix each one — TZ=GMT eduction -v ...

This should work on Mac OS X as well. I only have a vague outdated notion of Windows, but documentation suggests the same thing should work there.

It's a shame the standard doesn't encode the timezone!

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