Ask HN: How to capture screen output from a virtualized container?

Please excuse me if this post is really ignorant. Lately i've wondered, how, if its possible, to capture the screen output from a docker image running on a GUI-less debian distro. Is this even possible? How would the process work under the hood?

I am assuming that the app running inside the docker image needs access to the native GUI libraries for rendering, etc... Are these libraries availabla even on the GUI less linux distros? From there on I am completely lost at how I would actually run the image and capture the screen.