Something of an old article, but it raises several points I'd like to address.
http://www.dailymail.co.uk/news/worldnews/article-1162659/Students-tie-56-camera-balloon-send-edge-space-capture-stunning-images-Earth.htmlFirst off; the balloon itself.
If the disc that is the Earth is constantly accelerating upward, how does the balloon rise upwards (or any balloon ever made, or blimps, or planes?). Bear in mind that if you're using the Earth's constant upward motion to account for the downward tendency of dropped objects, it also must be applied to balloons, planes, etc.
Secondly; range of vision.
There is a horizon that the camera captures, the 'field of vision' so to speak, and as it increases in height, more of the landscape is revealed; things originally beyond the horizon come into view, something that makes perfect sense in a round Earth, but is questionable on a flat earth.
Thirdly; curved horizon.
Why is the horizon curved? Pay careful attention to the picture, where the curve is upwards. Viewing a flat earth from a lateral perspective, as the camera is, would not be possible were the Earth flat, even as a 'disc'.
Discuss.