https://medium.com/@neshpatel/solving-sudoku-part-ii-9a7019d...
Basically, you are cropping the image and saving it - which even a crappy cropping tool does. Do not consider this as a discouraging comment - programming can do better.
I understand you are looking for jobs and trying things. If I'm the hiring manager, I would rather prefer a candidate who found puzzle coordinates from the image bits/pixels and suggest cropping regions.
I am just exploring the OpenCV library for fun things to do and in the process documenting simpler and smaller stuff for my reference. I do plan to have a follow up post that will automatically find the corners!