Reliability of information returned by DateTimeOriginal

[Dan Lewis]

I'm trying to use the time extracted from DateTimeOriginal. The time seems correct when the device is a smartphone -  probably because it gets the time from a GPS or Internet connection. However, I find that the time reported by other devices is often incorrect (perhaps because an incorrect time was entered manually). I'm hoping that someone with a lot of knowledge about digital cameras can answer the following that would help me determine how reliable the reported time is:

Question 1: I assume there are cameras other than smartphones that also have a GPS or Internet connection. Is it reasonable to assume that a device has such a connection if it reports a value for OffsetTimeOriginal?

And two questions about cameras WITHOUT a GPS or Internet connection:

Question 2: Are there cameras that automatically update their internal date and time whenever they are connected to a computer (e.g., to download photos)? Is there any EXIF information that would say?

Question 3: Are there cameras that automatically adjust the time for Daylight Savings based on the date? If so, how does they handle states like Arizona and Hawaii that don't observe DST, and is there any EXIF information that would say?

Thanks!
Dan

[StarGeek]

However, I find that the time reported by other devices is often incorrect (perhaps because an incorrect time was entered manually).

For any file other than a cellphone or a DSLR that has a GPS add on, the date/time is only as correct as it has been set in the camera.  I had a friend that once set his camera 12 hours off (AM was set as PM and vice versa) and I had to correct a year worth of photos. And with another friend, the clock on his point and shoot camera reset every few minutes, so every single shot was shot on January 1, 1980, between midnight and 1 am.

Question 1: I assume there are cameras other than smartphones that also have a GPS or Internet connection. Is it reasonable to assume that a device has such a connection if it reports a value for OffsetTimeOriginal?

Probably, though it's always possible that some of the newer DSLR cameras might set it based upon the settings in the camera.  I haven't checked to see if it's true. Or the file has been edited to include the offset time. And such things are always subject to user error.

Most (all?) DSLRs include a setting for the local time zone and whether it was Daylight time or not, and record these settings in the MakerNotes.  And you usually have to manually trigger Daylight time.  In Nikon and Canon cameras, you set the time zone and leave it and the camera will adjust the time when you have Daylight time set.  For example, my Nikon includes this data

Code Select Expand

[Nikon]         TimeZone                        : -08:00
[Nikon]         DaylightSavings                 : Yes
Because DaylightSavings is set, every image will have the time adjusted by one hour, so I don't have to try and change the time correctly, I just flip the DaylightSavings setting.

Question 2: Are there cameras that automatically update their internal date and time whenever they are connected to a computer (e.g., to download photos)?

I have not heard of any camera that does this.

Is there any EXIF information that would say?

No. This probably wouldn't be something that would be saved.

Question 3: Are there cameras that automatically adjust the time for Daylight Savings based on the date? If so, how does they handle states like Arizona and Hawaii that don't observe DST, and is there any EXIF information that would say?

No, I don't believe there is.  There is just too many problems with time zones to do this, as they are always changing.  My obligatory link Tom Scott's The Problem with Time & Timezones video link.  There's an example in that video where one part of the population is on a different time zone than the rest of the population, in the exact same location.

Basically, you can never assume that any tag in a file is 100% correct. User error can happen and the file can always be edited.  You can only work with what data is in the file.

[Dan Lewis]

Hi StarGeek,

Thanks for the fast response! That's what I suspected. Oh well....  :-)

Best,
Dan

[wywh]

AFAIK the newest GPSTimeStamp is grabbed when a GPS-equipped device manages to get it from the satellite. For example, when the device is brought outdoors.

Some iOS ~13.2.2 and later devices do not have GPSTimeStamp anymore, only GPSDateStamp, and the GPSTimeStamp offset is moved to 'OffsetTime*' tags. But not all iOS devices or iPadOS versions seem to behave the same.

Our district heating control panel in the basement can an adjust the time for Daylight Savings based on the date...

- Matti

[Hubert]

Just to add my tuppence worth...

Question 1: I assume there are cameras other than smartphones that also have a GPS or Internet connection. Is it reasonable to assume that a device has such a connection if it reports a value for OffsetTimeOriginal?

Very few as far as I'm aware. I'm a Panasonic user and the venerable TZ30 and TZ40 (ZS30 and ZS40 in the US I believe) did have built-in GPS. They have long since been superseded, and newer models (eg my current TZ90) rely on a live Bluetooth connection to a Panasonic smartphone app to write geotagging data to images. In all cases the time (including daylight savings) must be set manually in-camera. If you forget to change daylight savings in the camera, then it's ExifTool to the rescue...

Question 2: Are there cameras that automatically update their internal date and time whenever they are connected to a computer (e.g., to download photos)? Is there any EXIF information that would say?

Couldn't say for certain but not that I'm aware of.

Question 3: Are there cameras that automatically adjust the time for Daylight Savings based on the date?

I very much doubt it.

[Dan Lewis]

Hi Matti and Hubert,

Thanks for responding. 'Seems like the concensus is that probably the most reliable times will be those accompanied by OffsetTimerOriginal. I suppose I'm not very surprised and will just have to add a disclaimer on my website about the time values.  :-(

Best,
Dan

[StarGeek]

It should also be noted that the offset time zone tags weren't added to the EXIF spec until July 2016 and only started to show up written by cameras around 2020. I have a post somewhere in my history where I first noticed it.  So any file with a time stamp of 2016 or earlier has definitely been edited, and any file from 2016 to 2020 has probably been edited.

Edit: Found it.  Offset time tags were first seen, at least by me, in June 2018 from a DSC-RX10M4 camera.