Some useful links

For build a mobile document scanner

https://www.pyimagesearch.com/2014/09/01/build-kick-ass-mobile-document-scanner-just-5-minutes/ https://www.pyimagesearch.com/2014/08/25/4-point-opencv-getperspective-transform-example/

For draggable points

http://www.hangge.com/blog/cache/detail_1057.html

For opencv.js

https://docs.opencv.org/3.4.0/de/d06/tutorial_js_basic_ops.html

Demo