How could it be an invisible vehicle? It's in the sky...
Anyway, I used my phone so I don't know how great the pictures will come out, although it does have 2.0 mega pixels.
Some prick kept killing me when I was trying to take it and it took at least five rounds to get two decent pictures.
The best chance you have of seeing it is near the barn when looking towards the terrorist spawn one. Look at it so that it appears against the solid colored mountains in the distance.
I took the pictures from spawn one because I tried taking it from the barn area but kept getting killed. I guess it's my fault for joining a room with 31 people in it...