I set my own background picture for the login screen using:
Admin -> Site configuration
Then upload it using “Upload your background image or enter the URL:”
This worked and stayed between updates. But after fixing a different issue (had to revert patches a few times for testing purposes) I noticed that the background image had been “deleted” as well.
Am I correct in assuming the background image is actually stored inside the docker-image and this gets overwritten with a new version or when issuing " docker-compose rm -f " as mentioned here: