Visual cues. People working in a remote area on a grainy black-and-white photograph is automatically associated with concentration camps and forced labour, because your brain makes this connection once you learn about the Nazis at school or during a TV documentary. It is the same mechanism through which people are scared of a yellow barrel with a radiation symbol, even once they realise it only contains pencils and papers which were used in the control room of a nuclear power plant and were put inside there due to nuclear regulations