On the archive.org website I have found two books showing the musical instruments collection of a museum in Cöln (Cologne).
The second volume of the catalog describes the plucked instruments. For this article I have selected the mandolin family and extracted the pictures. The quality of those pictures is not the best, but they are very interesting anyway.
Musikhistorisches Museum von Wilhelm Heyer in Cöln : Kleiner Katalog der Sammlung alter Musikinstumente, verfast von Georg Kinsky