How can you be certain they were not all taken by aircraft?
I doubt aircrafts can take pictures of that height.
Well, suppose the aircrafts are covering one area by taking a lot of images and then pussling them together to a larger picture (the whole). Since the images are updated every few hours, I guess they would have to send out new aircrafts all the time.
It's more realistic in every aspect that the pictures are taken by satellites. The nature of the pictures can testify for this too.