HUAK
This is some socialist celebration but I have no idea when the photo was taken. I can see that it took place on the Procession Ground near the City Park.
The Centropa archive has been acquired by the United States Holocaust Memorial Museum in Washington, DC.
USHMM will soon offer a Special Collections page for Centropa.
Academics please note: USHMM can provide you with original language word-for-word transcripts and high resolution photographs. All publications should be credited: "From the Centropa Collection at the United States Memorial Museum in Washington, DC". Please contact collection [at] centropa.org.