Hi Marcin,
this is a complex issue and i don't think i can cover it with some sentences.
But there is a new book about the imperial german aviation comming out the next months. I have this info from the author. I'm sure this book answer all your questions. I will write more when i get infos from the author.
If you are interessted on this topic you should spend the money for this book.
Regarding the identification of personal on pictures is more difficult. There are no guidlines how to distinguish this. It depend on the situation and on the hints from the picture itself.
Regards
Alex