* Buy a GoPro
* Buy weather balloon; you want something that will go at 80,000 feet up, and has GPS tracking so you can recover the balloon later.
* Tether and fill weather balloon
* Hang camera from weather balloon, pointed down
* Press record
* Release balloon
* About two hours later, the camera will land. Drive to its location and pick it up.
* Review video. If the earth is concave, it should look like your mockups. If not, it will look like a very large ball.