Those last two (Alien ones, as this comment will make no sense if you add more) should get Geoff started. :)
Geoff said 1 day later
I already informed GJ that the aliens had enabled their cloaking shields in the second photograph. I just used some simple, scientific deduction to draw my conclusion. If you notice in the second picture, the clouds are somewhat distorted by the saucer figure. Only a trained eye could catch such a subtly.
