The following is an image analysis of a screenshot from a flat earther video who shows this video as prove of a flat earth. I will show how the flat earther deceives people by presenting distorted images as prove of a flat earth.
The top image is the unedited screenshot from the video. We can see that all straight vertical lines are bent because a fisheye lens was used. Any line below the center of the frame on an image taken with fisheye lens is curved outward from the center. If we compress the image horizontally (see left stripe) we would see a curve in the horizon, if there is any.
Here we see a concave curved horizon. Even flat earther have to admit, that this is not the shape of the earth. Consequently the footage does not show the real shape of the earth and is deceiving.
In the lower part I applied a lens correction in Adobe Lightroom. Now the previously bent vertical lines appear as straight as they are in reality. So this image is no more distorted and shows the real geometry. I again compressed the image horizontally to exagerate any curvature of the horizon, if there is any. And, lo and behold, we can see a convex curved horizon.
Source On the level - Step Up (with subtitles) by Beyond the imaginary curve
Wideangle lenses create so called barrel distortion. Straight lines are bent away from the center of the frame and get curved, except if they cross the center of the frame. We can see this effect clearly at the vertical lines, which appear bent outwards.
On the other hand, lines that are curved towards the center get straightened. So a convex curved earth horizon that lies below the center of the frame appears flat if it is on the right position in the frame.
See Lens Distortion and the Curvature of the Earth how lens distortion cgange the shape of lines.
Lens distortions can be corrected with software. I applied a lens correction that made the curved vertical lines straight. This compensated the barrel distortion and all straight lines are now straight. Curved lines appear now curved.
Note, in lens corrected wide angle images geometric shapes at the edges are still distorted. But this is a perspective distortion which keeps straight lines straight. We see an elongation of the womans head, which is typical for wide angle perspective. The horizon is near the center of the image and therefore not distorted in the lower image. It shows a slight curvature as expected from this height.