I created a program using Python and OpenCV where a user can click on 4 points in an image and the program will return the coordinates of those 4 points. If the user presses ‘c’ after the points are selected the program will print the coordinates of the points. If the user presses ‘r’ the previous selections will be cleared and the user can select 4 new points.
Here is a link to a folder with the program and images in it. You have to download the entire folder and run the Python program from within it.
An image of the output: