UTC in iphone metadata independent of local time zone choice

[Duncan Carlsmith]

I believe offset tags provide UTC time independent of user choice of local time zone.

I set my iPhone 13 pro time zone in preferences to London (GMT+1 just now), and took a photo in Madison WI (CDT just now and =GMT-5 hours), mailed it to myself immediately, opened the mail on my laptop (with its timezone local to Madison, WI), and ran exiftool. I find

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Exiftool
Now                            : 2023:07:01 07:43:08-05:00(correct CDT per laptop processing, UTC can be correctly computed noting the offset -5:00 means MSN is GMT-5. It does not mean subtract 5:00 minutes or 5 hours from 07:43:08! The UTC is the local time minus the (negative) offset in hours)

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System
File Modification Date/Time    : 2023:07:01 07:40:55-05:00
File Access Date/Time          : 2023:07:01 07:41:22-05:00
File Inode Change Date/Time    : 2023:07:01 07:41:20-05:00(correct local time from laptop)

MacOS (It think MD refers to mail handling)

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File Creation Date/Time        : 2023:07:01 07:40:55-05:00(correct UTC noting the offset -5:00)

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MD Item Content Creation Date  : 2023:07:01 13:39:49-05:00
MD Item Content Creation Date Ranking: 2023:06:30 19:00:00-05:00
MD Item Content Modification Date: 2023:07:01 13:39:49-05:00(strange)

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MD Item Date Added              : 2023:07:01 07:41:20-05:00
MD Item FS Content Change Date  : 2023:07:01 07:40:55-05:00
MD Item FS Creation Date        : 2023:07:01 07:40:55-05:00(correct)

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MD Item Interesting Date Ranking: 2023:06:30 19:00:00-05:00(hmm, wonder what this is!)

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MD Item User Downloaded Date    : 2023:07:01 07:41:20-05:00

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IFDO
Modify Date                    : 2023:07:01 13:39:49(local London time not UTC)

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ExifIFD
Date/Time Original              : 2023:07:01 13:39:49
Create Date                    : 2023:07:01 13:39:49
Offset Time                    : +01:00
Offset Time Original            : +01:00
Offset Time Digitized          : +01:00(London local time and offset subtracted gives UTC)

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Composite
Create Date                    : 2023:07:01 13:39:49.938+01:00
Date/Time Original              : 2023:07:01 13:39:49.938+01:00(London time. Most accurate as it includes the subsec value and will give the correct UTC)

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Modify Date                    : 2023:07:01 13:39:49+01:00

[StarGeek]

Is there a question here?

All the data show seems to be accurate. The EXIF time stamps in IFDO and ExifIFD are supposed to be set to the local time where the image was taken, not UTC.  The EXIF standard splits the date time stamps into three separate tags where the main date/time is in one tag (CreateDate, DateTimeOriginal, and ModifyDate), the subseconds (SubSecTimeDigitized, SubSecTimeOriginal, and SubSecTime), and finally the time zone (OffsetTimeDigitized, OffsetTimeOriginal, OffsetTime).  Exiftool will combine all the three tags into a composite tag to make it easier to copy full time stamps (SubSecCreateDate, SubSecDateTimeOriginal, SubSecModifyDate).

The MDItem* tags are part of the Mac file system and do not exist in the file.  They will be lost when a file is copied to a non-Mac file system or uploaded via http.