MATCH

feature matching in the browser — nothing is uploaded
Sentinel-2 is 10 m and free to use commercially, which the sharper basemaps are not. Expect weaker matches than against sub-metre imagery — a 10 m reference cannot resolve what a 2 m photograph shows.
Your images never leave this machine. They are read into a canvas and matched on your own GPU — which is also why there is no server bill behind this page. Fetching a reference does send the location you gave to AWS Open Data, because that is how it knows which scene to return; the photograph itself is not sent, and choosing your own reference sends nothing at all.

, reduced to 1024 px for matching. A full CORONA scan needs the desktop tool: tiling a 100 Mpx strip and warping it with GDAL is not browser work.
Shear says whether an affine was the right model: near zero means the pair differs by little more than a scale and a rotation. A large value means the ground is tilted or the lens is wide, and the transform this page fits is not enough.