These quartered circles are mainly used as alignment aids during capture, to help you keep the camera perpendicular to the surface and avoid oblique-angle distortion in the first place.

Post-capture correction is possible, but it is not as simple as “make the ellipse a circle.” The general process is called rectification. In image-editing software, a basic approach is to place a true circle on a separate layer, then transform the image so the photographed target matches that circle. However, this must be done carefully, because correcting one area can introduce distortion elsewhere.

That’s why, especially in scientific or forensic work, image correction is treated cautiously and usually requires additional checks such as verifying scale and other reference measurements to avoid creating new errors.

So in practice: the targets are primarily there to help prevent misalignment at capture, and only secondarily as references for controlled rectification if correction is necessary.