Thanks for the replies.
I have already done what @bluepuma77 said (Tried in another PC with an UBuntu Desktop). Then I guess I only need to launch a web browser in full screen automatically and connect throught localhost.
I was trying to avoid this idea because I guess it uses more resources and seems less “professional”. I would try to replicate the video (sorry it is in spanish, Im from Spain 
) but this time in an Ubuntu Desktop. Basically, display directly what Docker is running.
For the project, it is compulsory to display those images in real time and store them, preferably all in one PC. It will also show other things in the future.
I connect using SSH and I have also tried to use the command echo locally without luck.
Just to fufil my curiosity and to investigate a bit. Would it be possible to display something trying something like this if my OS is only a terminal (without gui, I dont know if it the proper term)? Or I should give up?:
docker run -d --name firefox -e DISPLAY=$DISPLAY -v /tmp/.X11-unix:/tmp/.X11-unix firefox
Theorically, I have X11 server files and they are running. What I cant find is how to make the PC recognise the display. I remark, there is a display connected through VGA.
If X11 is the manager of the display and I let Docker access to them, it should work although there isnt gui in the base OS, right?
Edit: I forgot to mention, the purpose of having the UI inside Docker is to prevent that in a crash event it freezes the whole system. So, in case of fail the automatised process works as normal. That’s why I’m not coding a python program outside Docker with access to the Redis server (how the photos are sent), that manages all the UI. Of course, this in an desktop enviroment. I dont know if Pygame or a similar library of python works without gui.