ddt83

A question I had was how he made the correspondences between points in the two bolts. I have a hunch that he just traversed the two lightning bolts separately and said point 1 in A corresponds to point 1 in B, ... Point N in A corresponds to point N in B, etc. if this is the case, you would expect dx and dy to grow as from top to bottom and hence his reconstructed depth to become closer from top to bottom, which is what happens.

Right, image segmentation is the correct terminology. Background subtraction is incorrect. I don't think it's quibbling to point that out.

I agree. I was pointing out that background subtraction is not the same task.

I will not debate common language use of 'background subtraction' because I have not discussed it with laypeople before, but what I can say is that if you were trying to implement what the article is trying to implement and were trying to find relevant literature, then searching for background subtraction would not turn up anything useful.

Background subtraction operates on video streams, not still images, so this is incorrect.

I don't think background subtraction means what you think it does. Background subtraction refers to the subtraction of neighboring frames of a video sequence in order to find moving objects in a video sequence. So, yes segmentation is a more general and difficult problem than background subtraction, but it is in no way relevant to the task described in the article.