Most pictures of the earth taken by amateur balloonists at very high altitudes are not doctored. Flat Earth Theory holds that there is elliptical curvature from the edge of space. Any photograph showing a curved elliptical horizon from very high altitudes poses no affront to FE.
Curvature results from the fact that at the edge of the atmosphere we are looking down at the illuminated circular area of the sun's light. The observer is looking down at a circle. A circle is always curved in two dimensions. When looking down at the circular area of the sun's light upon the earth we see elliptical curvature.
Under the assumption that this image is rectilinear and unwarped by a camera effect, we directly observe in the image is curvature in two dimensions, a circle. We are asked to imagine that we see curvature in three dimensions.
Why can't we see all of the continents of the earth from the edge of space?
Although the observer is looking downwards at the circle of the sun's spot of light, the distant continents of the earth are still thousands of miles away horizontally from the observer, and thus beyond the resolution of the human eye and merged with the line of the horizon, squished into indiscernibility 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. The far distant horizon, upon which all is squished into imperceptiveness, is only sending light from which the rays of the sun reach. The darkened areas around the curve is night.
A View from Everest