Guys, I hope you don't mind when I enter the Open House with a biplane that I'm unable to identify.
The photo is on a French or maybe Belgian Postcard ("Carte Postale" on the backside).
At first look i thought this biplane might be East-European, the elliptical wings with its pointed wing tips look similar to some Polish types. However, I couldn't find this aircraft in the book "Polish Aircraft 1893-1939"
I had a look in the following books as well, without result:
"Romanian Aeronautical Constructions",
"L'Aviation Legère en France 1920 -1942",
"British Light Aeroplanes",
"Aviones Espanoles del Siglio XX"
"Das Buch der deutschen Luftfahrttechnik"
At aviadejavu I went through any single-engined biplane (except for Russia and Japan) from 1920 to 1939, also without success.
The engine looks like a Walter Mars I when compared to e.g. an ANBO 3 (
https://www.plienosparnai.lt/e107_files/public/1570131221_2_FT5196_anbo_3_003.jpg), but that didn't help me as well.
Below the wing it looks that there might be the letter "D" or "O", but that is not 100% certain. If true, possible registrations would be from Germany, Belgium, Denmark, Finland or Tchechoslovakia.
I hope with the combined knowledge of this forum we are able to identify this mystery. Any suggestions?