Why does my iPhone photo show the wrong time when I travel?

Open Settings → General → Date & Time. With Set Automatically on, the iPhone takes the time from the network and the time zone from where it is; the zone can only update by itself if the phone can tell where it is, which needs Location Services. If Set Automatically is off, or the zone is set by hand, the phone keeps your home zone after you land and every new photo is stamped with the wrong local time.

Check the zone while you are still at the airport. The wording of the settings, and whether the time zone follows a separate System Services switch, can differ between iOS versions.

A photo records an instant. How that instant is shown as a clock time depends on which time zone the viewer uses. A photo taken at 9:00 in Hanoi is 4:00 in Paris in summer and 19:00 the evening before in San Francisco. One app may show the time where the photo was taken; another may show it in the time zone of the device you are holding. Both are "correct", and they disagree by hours.

How the Photos app on your iPhone chooses, and how Photos on a Mac or iCloud.com chooses, has changed between versions and people still report differences, so do not assume. Compare the same photo on two devices before you trust a time.

The classic EXIF date field, DateTimeOriginal, is a plain clock reading with no time zone. A separate, newer field can hold the offset from UTC, but not every app writes it and many ignore it when reading. So when a photo goes through a messaging app, a social network or an editor, the time may be dropped, replaced with the time it was sent, or reinterpreted in the zone of whoever opens it.

A screenshot, or a photo saved from a chat, carries the time it was made or saved, not the moment of the original shot.

In Photos, open the photo, swipe up (or tap ⓘ) and tap Adjust. You can change the date and time, and on current iOS versions the time zone too. To fix a whole trip, tap Select, choose the photos and use Adjust Date & Time from the more (…) menu, which shifts them together by the same amount. The exact buttons depend on your iOS version.

Only do this to correct an honest mistake, such as a phone that kept the home zone. Do not change times to make a photo say something it did not happen at.

• Before you take the first photo, check Date & Time shows the right local zone, and recheck after each flight.
• If photos from a camera or a second phone are mixed in, shoot a photo of a clock or of the phone's clock screen once, so you can see how far each device is off and shift the batch.
• When the time matters to someone else, tell them the zone with it: "9:00 Vietnam time (UTC+7)". Do not rely on the file to carry it.
• For a record that has to be read without any viewer's guessing, the time can be printed on the picture itself, as part of the image.

A time printed onto the picture is read from the phone's clock and zone at the moment of the shot. If the zone is wrong, the printed local time is wrong by whole hours even though the instant is right. Check the zone before shooting check-in or delivery photos, and see the guide on a wrong clock if the minutes are off.