I don’t know where to start / where to read the creation of the program, measuring the length in the photo ??

Question

Python

You need to create a program that will:
1) Load an image
2) mark two points at the user's request
3) measure the distance between points on this straight line in a tricky way: the pointer will move at a given speed, and pressing a button (any) will display the distance between the previous and new point in pixels.
I do not know where to start, what to read, I will be grateful for the tip.

Answer 1

There are several options. Use Qt-python.
Use sciphy - www.scipy-lectures.org/advanced/image_processing Use
PIL/Pillow - https://habrahabr.ru/post/247219/ and pillow.readthedocs.io/en/3.3.x
points, draw a marker and move it over the image. Well, the length of the line can always be calculated using the Pythagorean theorem - a**2 + b**2 = c**2

Answer 2

Windows API and any add-on: request mouse coordinates, distance (see Aleksey Cheremisin) using the Pythagorean theorem.