One of the best examples, we reckon, is the allied aerial reconnaissance material of the Nazi secret research facility at Peenemunde on Germany's Baltic coast. Back then they had teams of highly-trained operatives poring over photos with magnifying glasses trying to work out just what Adolf was up too. Tricky work, as this image shows:
Well, what would you have made of it? By 1943, the RAF had made enough of it to produce this bombing map:
To have a look at Peenemunde now on Google Earth (with the bombing map overlaid - a nice touch provided by Google Earth Hacks) - try this .kmz link. Bear in mind that most of the wartime facilities are now gone - systematically destroyed by the Russians.
If you compare the reconnaissance snap with the map, you'll see just how little info the bomber crews were provided with. This is either by design, since the government didn't want it getting about that the Nazis were developing a rocket capable of hitting London, or because they simply didn't know exactly what was going on.
Try the structure marked "A" on the bombing map, though, and then have a closer look on the photo (marked "A1" by the RAF - that's our big white arrow). In fact, the allies already had a pretty good idea what the "experimental station" in question actually was.