Custom map In UMAP

Hello Forum (lurkers :P)

One of the info sites of a game im playing (entropia universe) has an interactive image map using UMAP

http://umap.openstreetmap.fr/en/map/new-planet-cyrene-by-thanatos_31859#2/-33.1/-8.3

He uses a custom image as background and I was wondering how you could make it!
I have tried everything and still cant figure it out…

this is the image as backgroung: http://nikander100-testsite.weebly.com/uploads/3/9/6/2/39622757/9501398_orig.jpg

Kind Regards,
Nikander100

May perhaps be related to https://help.openstreetmap.org/questions/46949/umap-popup-does-not-show-my-image .

/i can give you an example of a custom map i want to crate a map like this one http://umap.openstreetmap.fr/en/map/new-planet-cyrene-by-thanatos_31859#2/-13.9/-12.8 , where can i import the jpg file into the map editor so it shows the jpg as an map in UMAP?
or does it need to be a cvs, kml file?