Quick easy and (somewhat) effective commandline tool that'll subtract and/or add a background into an image.
Certainly easy to use, can operate on a single file or entire directory, and it more or less handles multiple foreground subjects.

I'm seeing okay-not-great results when backgrounds are complicated, or subjects are wearing a color that's common in the background.

https://opensource.com/article/23/4/image-editing-linux-python