[digiKam-users] Is the "image already scanned" Property Available as Metadata?

[Farblos]

Hi,

I'm in the process of migrating from Windows Photo Gallery to digiKam 
(using my tool github.com/farblos/wpg2dk).

In the People View -> Detect Faces there is that option "Skip images 
already scanned".

Now my questions are:

1. How does digiKam know that an image is already scanned?  By the 
presence of any face regions?  Or is that an extra flag in the image 
database?

2. If the latter, can one set that flag of "already being scanned" 
somehow per JPEG/XMP metadata?  So that images completely done in WPG 
would not need to be scanned again for face detection.

Thanks

Farblos