How to fix EXIF data on Google Photos exports

Google Photos doesn’t save date/time changes, descriptions, or GPS data set in-app to the photos’ EXIF data. Instead, when using Google Takeout this information is exported as JSON sidecar files (apparently Google had to bikeshed something rather than just using XMP).

Fortunately, ExifTool can merge the data from these files back into the exported photographs:

exiftool -r -d %s \
         -tagsfromfile "%d/%F.json" \
                       "-GPSAltitude<GeoDataAltitude" \
                       "-GPSLatitude<GeoDataLatitude" \
                       "-GPSLatitudeRef<GeoDataLatitude" \
                       "-GPSLongitude<GeoDataLongitude" \
                       "-GPSLongitudeRef<GeoDataLongitude" \
                       "-Keywords<Tags" \
                       "-Subject<Tags" \
                       "-Caption-Abstract<Description" \
                       "-ImageDescription<Description" \
                       "-DateTimeOriginal<PhotoTakenTimeTimestamp" \
         -ext "*" -overwrite_original -progress \
         --ext json $GOOGLE_PHOTOS_DIR

Note that this will fail for any photos with a timestamp before 1970; for these photos, replace "-DateTimeOriginal<PhotoTakenTimeTimestamp" with "-DateTimeOriginal<PhotoTakenTimeFormatted" -d "%b %d, %Y, %I:%M:%S %p UTC".