Farm subsidies in the EU cost taxpayers billions of euros each year, and so it's naturally in the best interests of regulators to maintain tight oversight over who gets how much. For years now, regulators have relied on satellite imagery to help them keep an eye on those claiming subsidies, photographing farmland from above and looking for the telltale signs of subsidy cheats or breaches of environmental rules. But satellite images are unreliable. In some places, mountainous terrain makes for long shadows that obscure features on the ground. In places like Scotland, it's overcast all the time.