Bogdan is correct. The XMP specification stores all date/time strings
in ISO 8601 format, which requires a timezone indicator to be specified.
This is different than the EXIF specification which has no timezone.
As of ExifTool version 7.04 (released Dec. 3, 2007), the date/time values
are coerced into proper format when writing unless the -n option
is used. If a timezone is required but not specified, exiftool adds one.
Up until now, exiftool has added "Z" to satisfy this requirement, but
upon reading the XMP specification again, it suggests adding the local
timezone if no timezone information is specified (ie. "-05:00" would
be added instead of "Z" if your local timezone is EST). I will make this
change and exiftool 7.15 will add the local timezone instead of "Z"
if the timezone information is missing.
If you the timezone where the pictures are taken is different than
the local timezone, you can specify a timezone when copying information
like this:
(4)
]
