Unique Photo Identifier when using multiple iOS devices

I'm having a friend using my Nextcloud instance for uploading and storing photos when she is on holiday. She still uses iCloud Photo and she has two devices. With this combination, the following annoying behavior occurs:

Photos are upload from both devices. Not only the photos shot on the devices, but also the photos synchronized by iCloud photos.
The photos get uploaded with different filenames as the id added to the file name is not the same.

Expected behaviour

Photos uploaded from iOs devices that has been synchronzied shall be detected and handled as the same photo.

Actual behaviour

Photos uploaded from iOs devices have different file names.

Filename is e.g. 21-12-05 16-05-10 AFGD.jpg where AFGD seems to be an id or counter on the device.

Reasoning or why should it be changed/implemented?

It would save space as photos may be uploaded twice, but overwritten, so not appearing twice on Nextcloud.

I wonder if there is an id in the photo roll or the meta data of the photos that could be used instead of a counter. iCloud photos itself must handle something similar so maybe we could also use that id for the filename?

A wonderfull solution would be something that could track uploaded photos on all connected devices so photos are not uploaded twice or an option to upload only photos taken on the device itself. Unsure if the information for that is available in iOS for a Non-Apple-App.

nextcloud / ios