This a usability improvement proposal. 

If you have not used digikam before, when you do some face detection and the process finishes, there is nothing that indicates you that something has been done. I thought it just crashed and the feature didn't work.

Only after casually browsing the face list, I realized there was a tag called "Unknown" inside the "People" tag. I have 800-900 different people in there, it was not intuitive to search for unknown faces in the letter "U" amongst hundreds of faces, because the list is sorted alphabetically.

I propose that the "Unknown" tag should occupy a more visible and preeminent location in that list, maybe placing it on top of it, and using a different format (since it's not really a proper face tag, it's something else). It would even be a good idea to be always visible when scrolling the tag list, so it always stays visible (this is what Picasa does, if I recall correctly).