Behind every powerful AI system are huge numbers of people labelling and clarifying data to train it, contracted by companies like Remotasks, a subsidiary of Silicon Valley-based data vendor Scale AI, whose customers include the US military and OpenAI. Often the workers, who are assigned tasks they don't understand for a purpose they don't know, are sworn to secrecy. Yet labelling is crucial; it can make the difference between a car stopping to spare the person walking a bike across the road or…