A good majority of pictures of Earth taken from space are being dismissed by flat-earthers merely because they are made using fish-eye lenses. They believe any curvature of Earth shown in those pictures is the result of the fisheye effect, and thus, cannot be used as evidence of Earth’s curvature. They even take a step further and assume a fish-eye lens is deliberately used to take every picture of the Earth taken from a high altitude so that they would have a curvature in it.
These claims are, of course, ungrounded. In some cases, we can conclude the curvature is there, even when a fish-eye lens is being used. We can use this useful property of any photographic lens:
A straight line will appear straight as long as it crosses the center point of the image.