Regarding Elixir camera that tracks a movement:
Here is a small example for similar project.
You can also see the example of its work here: Elixir Smart Home - 047 Daemonize CCTV application and send Telegram notifications - YouTube
It does not use Nerves, but you can port it to some board if required.
I have also started to create Elixir Smart Home solution. Here is an Elixirforum thread for it. The project is in early stage now.