How can I capture a video stream from a Windows window using Python?

Question

Python

I'm trying to capture a window for further processing of frames.
I tried to capture a picture through OpenCV and ImageGrab from PIL.

The problem is that when using these methods, the window comes to the foreground (if there were other windows in front of it) and after that the screenshot is written to disk - and this is not necessary, since the task of the script, roughly speaking, is to take the window and each frame in real time overlay a watermark image at a certain position