At eBay
here is an Avia B-534.IV. The stkz is only partially visible, but from what can be seen I cannot find a known stkz which appears to match this one. The aircraft has an emblem which I do not recognise. The photo is a postcard, which has a date of 14 Sept 1943. This hopefully provides a rough date for the photo. I would suspect that the aircraft belongs to a schleppe (glider towing) related unit. However if this was an operational unit I would expect yellow noses and or tails. There is no sign of this. I think then this could be a Ergänzungsgruppe (S) 1 or 2 aircraft. Does this emblem match these units?
There is also a message on the postcard which might help if translated.
Cheers
Ian