Hi there Theodor...
The code 1Z+?? belonged to:
- KGrzb V 1 (from October 1937)
- Later became KGzbV 1 (from June 1939)
- Later became TG 1 (from May 1943)
Depending on the date of the image, with regards the last two letter of the code:
G = red individual aircraft letter
Y = 14 Staffel, V Gruppe or 14 Staffel IV Gruppe
[source: "Luftwaffe Codes, Markings & Units 1939-45" by Rosch, Schiffer 1995]
Cheers
Peter D Evans
LEMB Administrator