How does Google Photos recognize the real date the photo was taken

Started 3 months ago | Discussions thread
techjedi
techjedi Veteran Member • Posts: 4,087
Store in UTC, display in local
1

asafa wrote:

I uploaded to Google Photos a photo taken in Florida with NIKON COOLPIX S3500 (without GPS).
Whe I took the photo, the time zone of the camera was still Italian and the DateTimeOriginal of the photo (also verifying with Exiftool) it is 30-June-2015 at 03:57.
But after uploading to Google Photos, the photo is listed under the date 29-June-2015 (although the Google Photos information on the date of the photo still looks like: 30-June-2015 03:57).
In reality the photo was taken in Florida on 29-June-2015 at 21:57.
How does Google Photos recognize the real date the photo was taken (29-June-2015) when the photo file shows DateTimeOriginal = 30-June-2015?

Most systems store the date in UTC format and simply display to you the date/time applying your current time zone's adjustment from UTC.

The photo's UTC time is correct regardless of where it was captured. When you uploaded, there is a chance you uploaded from a web browser in florida's time zone, so Google is just converting the native UTC to Florida's time. If you were to open a browser with Italy's time zone, it might show the adjustment to that local time.

To further confuse this, sometimes both variations of the datetime are recorded and some systems do the UTC adjustment and others just display the timestamp as is.

This behavior isn't limited to cameras, its a general standard in computing. An easy way to demonstrate this behavior is to create a file on your PC, look in file explorer and write down what is shown as the created datetime or updated date time. This will be displayed in your local time, while the file system recorded the UTC version. It is simply applying your timezone offset to the stored time. Then go into your system settings and change the time zone. If you go back to the file list, the datetime will update to show you what the UTC + offset would be for the changed time zone, etc.

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