- Video 4 Linux loopback device kernel module (
v4l2loopback) - Source: https://github.com/umlaeute/v4l2loopback (You might find builds in your distro's repos - I'm using Fedora so had to build it myself using https://github.com/danielkza/v4l2loopback-fedora/)
- gPhoto2 - this is what allows you to access your cameras live feed over USB - this was available in Fedora's repos.
- GStreamer or ffmpeg - this is what lets you stream the output from gPhoto2 into the loopback device.
It's been a little while since I set it all up so I can't remember all of the installation details, which will probably be different for your distro anyway unless you're using Fedora. Apologies if I have forgotten something as wel.