Hello,
Currently on ebay is a photo of a German Aircraft partial serial 198 at:
https://www.ebay.de/itm/Foto-PK-Flie...MAAOSwspZfFB9B
Tentatively, I'm tempted to identify this as Germania B.I LF.198,although a view of more of the aircraft would be useful to put it mildly.However the 198 being followed by a punkt rather than a slash appears like a Navy serial.
The Freiwilliger Marine Flieger Korps was based at Johannisthal. Diagonally to the left of the post mark there is handwriting in a thicker darker pencil. Would anyone care to attempt to decipher what is written? This might or might not help.
Regards,
Clint