This is an image taken in northern Wisconsin, USA.
I've extracted its EXIF data and the focal length of the lens was nominally 30mm, and which is considered a mild wide-angle lens.
Note that the horizon appears curved downwards a couple of degrees. Most flat earthers would assume that this is due to barrel distortion caused by the relatively wide-angle lens.
Only one problem.
If it was barrel distortion (which it's not) the horizon would appear to be curving upwards by a couple of degrees, because the horizon line is well below the lens's horizontal optical axis. What you're seeing here
could be described as "pincushion distortion" by a photographer only
if he was unaware of the focal length of the lens.
So the slight curvature one sees over an extremely wide expanse of water is definitely
not an illusion. The camera doesn't lie.