How To Use A Custom Map With Google Maps

Hi,
I’ve seen several websites using a custom image as a map with google maps controls.
I’m familiar with how to use the google maps api in general, but I don’t know how to use a custom map image that isn’t based on the real world, in other words it will be an image of a map from a video game, so general latitude and longitude wont apply.

Can anyone give me some advice please?

Is this what you’re looking for? http://www.maplib.net/