- https://en.wikipedia.org/wiki/Perspective_distortion_(photography)
- https://de.wikipedia.org/wiki/Stürzende_Linien – in German: “Stürzende Linien”
- https://learning.oreilly.com/library/view/the-book-of/9781457172410/ch16s02.html#perspective_tool – how to deal with perspective distortion using GIMP – from the “Book of GIMP”
- GIMP: Tools > Transform Tools > Perspective – it has a shortcut (⇧P), and also an icon in THE Toolbox
- https://en.wikipedia.org/wiki/Photoshopping