I’m no lawyer, but …
Taking the picture is not illegal and neither is putting it on the notice board, per se.
If it was posted with the intention of trying to identify the culprits so they could be “re-educated”, that’s probably OK too.
However, if the picture was pinned up with the proven malicious intention of embarrassing and humiliating the subjects and causing other owners or visitors to the building to think less of them, then you could find yourself on the wrong end of a civil defamation action.
Unlikely, I admit. But then so is going to all that trouble over a couple of cardboard boxes.
By the way, pixellation would have avoided the above while still achieving the “oh, that’s me!” effect.