I came across this post QGIS Georeferencer is stretching image whilst searching for information on georeferencing. The question links to an external website (with adverts) which shows three screenshots.
It's a good question and answer and so I am minded to edit the post to bring the screenshots into the question itself and remove the external link. This would to stop 'link-rot', and to bring it in-house, as it were. But it this the right course of action?
I have had a look on this Meta, and Meta SE, about this, and couldn't find a clear answer?