The flag is a red star, in a yellow circle, in a green ring, on a red background.
The photo is from a protest under the Polish presidential palace against legitimizing the Turkish president Recip Erdogan, organized by a left wing, out-of-parliament "Razem"("Together") party.
Searching on flags.net didn't bring any results and I suspect it has to be an unofficial flag.
There are two more photos available in the link, but I can't link to them due to low reputation.