I have some recent iPhone photos with timestamps in the wrong timezone. In Windows PowerShell,
exiftool -s -a -G1 *.heic | select-string 'date|heic' | select-string -notmatch file produces this for one of the files:
[IFD0] ModifyDate : 2022:10:20 15:44:34 [ExifIFD] DateTimeOriginal : 2022:10:20 15:44:34 [ExifIFD] CreateDate : 2022:10:20 15:44:34 [XMP-xmp] CreateDate : 2022:10:20 15:44:34 [XMP-xmp] ModifyDate : 2022:10:20 15:44:34 [XMP-photoshop] DateCreated : 2022:10:20 15:44:34 [Composite] SubSecCreateDate : 2022:10:20 15:44:34.263-03:00 [Composite] SubSecDateTimeOriginal : 2022:10:20 15:44:34.263-03:00 [Composite] SubSecModifyDate : 2022:10:20 15:44:34-03:00
The picture was taken at sea near a time zone boundary, and the iPhone got it wrong. The image was taken at 16:44:34-02:00, not 15:44:34-03:00.
I tried to fix this as follows,
exiftool '-datetimeoriginal+=1' '-offsettimeoriginal=-2:00' *.heic
but exiftool complains, "Error: Not a valid HEIC (looks more like a JPEG)". The files in question were downloaded from Google Photos, where they are stored in "storage saver" mode (i.e., lossily compressed).
How can I adjust the "when taken" timestamp(s) on these files?