How to use custom BG Image for kibana dashboards

I'm just trying to add custom Image to Kibana dashboard as a background just out of curiosity.
Can someone please help me out?

You could modify the source-code (https://github.com/elastic/kibana) and add some CSS with the background-image property filled in. This is a hack of course.

Feel free to file an enhancement request as well https://github.com/elastic/kibana/issues/new