After putting the system into headless mode and logging in via a laptop using SSH, I was able to test the system 'in the field'. Initially, there was a bug that caused the camera to turn off after 15 minutes and this was cured by installing 'screen' on the Raspberry Pi and typing 'screen' into the command line before initiating the python files. What screen does is it opens another terminal on the Pi, so it has it's own live terminal which does not get shut down when my laptop terminal shuts down. It's a really good solution and avoids having to mess about with other 'run on boot' solutions which can potentially wreck the whole system.
A separate video camera was set up in my office, 200 m away, synchronised with the main camera and focused on the receiver gadget (bottom right of video). On testing, the system did not respond to the dog in the camera frame, but did respond to me (a person) ….. Success!