“Visual daytime observations show that the minimum altitude at which curvature of the horizon can be detected is at or slightly below 35,000 ft, …Photographs purporting to show the curvature of the Earth are always suspect because virtually all camera lenses project an image that suffers from barrel distortion”
Another trick you can do: take this Concorde photo and use the rules of geometry to draw the rest of the circle, and look how small an Earth you’ve drawn.
Think of it this way: imagine you were in the middle of the ocean, just 100 feet above sea level. As you turned your head 180° to survey the horizon, do you think it would look curved?
