In that example, they're using OpenCV to display images and read from the webcam for a demo. At one point, they make it clear that OpenCV isn't used for any of the CV parts:
> We didn't compile Darknet with OpenCV so it can't display the detections directly. Instead, it saves them in predictions.png. You can open it to see the detected objects.
> We didn't compile Darknet with OpenCV so it can't display the detections directly. Instead, it saves them in predictions.png. You can open it to see the detected objects.