|Boeing plant aerial photo taken from around 5000 feet. This was taken in either 1944 or 1945. You can see the B-29s on the tarmac and other aircraft around the field.|
The idea of deceiving the enemy as to what you are doing is not new. Trying to hide individual items from observation is not new, trying to hide whole factories from aerial bombing during The Second World War was new.
After December 7, 1941 the Lockheed and Boeing aircraft factories along the West Coast were put under netting to try and hide them from Japanese aircraft attack. The Boeing plant went even further with fake houses and trees over the factory. The effectiveness of this was never tested - no Japanese aircraft got anywhere near these factories, but it did instill the sense of the war, the collective threat, to the people not on the front lines in those areas.
The Germans went to elaborate lengths to hide factories with netting and smoke screens - even so far as to build dummy oil refineries with similar reference points to fool bombardiers trying to hit it instead of the real factory a few mile further on - it actually known to have worked once.
However, asides from that rare case, hiding a factory would ONLY work if no aerial - or any type of images - of the factory was in possession by the enemy before the pre-mission photo-recon picture had been taken. Hiding a SINGLE item this big never worked - the bridges, rivers, prominent intersections etc would all still be there to allow a proper bomb drop on the factory. You have to hide everything around it within a mile so that the person toggling the bombs could not be sure exactly where it is. Off by 10 seconds means you miss the whole target. Thus you need to fake the scale in the camouflage or shift it over by 1/2 mile by making a new complete factory along with roads, intersections etc to match the original.