Hi again Mathias.
In case any of the following could help your investigaton
Attached is an image that shows that a "regular Windows" window exposes the unique serial number of the camera device (that is the case for all of my camera devices). As you can see it is a 32 character string.
This link describes the device properties that are supported by Windows Portable Devices:
https://msdn.microsoft.com/en-us/library/windows/desktop/dd319322%28v=vs.85%29.aspxSince the serial is very large maybe you could use, say, the last six digits for unique ID?
Perhaps code lines 235 to 238 here could also help:
https://fossies.org/linux/calibre/src/calibre/devices/mtp/windows/device_enumeration.cpp235 hr = keys->Add(WPD_DEVICE_FRIENDLY_NAME);
236 hr = keys->Add(WPD_DEVICE_MANUFACTURER);
237 hr = keys->Add(WPD_DEVICE_MODEL);
238 hr = keys->Add(WPD_DEVICE_SERIAL_NUMBER);
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