It's interesting that anyone can now buy a balloon and fly equipment into the upper atmosphere.
link: http://www.natrium42.com/halo/flight2/
We know about that already. Flat Earth Theory holds that there is elliptical curvature from the edge of space, one hundred miles in altitude. Any photograph showing a curved elliptical horizon from very high altitudes poses no affront to FE.
Curvature results from the fact that on a flat earth we are looking down at a circle. The Antarctic coast and other continents of the earth are still tens of thousands of miles away horizontally from the observer at an altitude of 100 miles (edge of space), and thus beyond the resolution of the human eye and merged with the line of the horizon, indiscernible and faded with the thickness of the atmosphere. This is why the view is limited to the immediate vicinity below the observer, and why the land fades into a blueish fog as it recedes.
We can confirm that we are looking down at the circle of the earth by noting that shots from amateur high altitude balloons show an elliptical horizon. If the earth were a globe, curving downwards in three dimensions, all curvature seen in photographs would appear as an arc of a circle. The only pictures which show the horizon as an arc of a circle are NASA's Apollo shots.