@ostfilinchen Hi there,
I also wanted to add background images to my MM and came across your post. Although it is not very recent, I think it might be a good idea to add the following information:

if you want to have additional folders to be available within the Mirror, you need to specify those in the /js/server.js just after the other app.use commands, e.g. :

app.use("/Images",express.static(path.resolve(__dirname + "/../Images")));

@ostfilinchen Hi there,
I also wanted to add background images to my MM and came across your post. Although it is not very recent, I think it might be a good idea to add the following information:

if you want to have additional folders to be available within the Mirror, you need to specify those in the /js/server.js just after the other app.use commands, e.g. :

app.use("/Images",express.static(path.resolve(__dirname + "/../Images")));