One of the map source types supported by Maperitive is a georeferenced image. Georeferenced image is a bitmap file (PNG, JPG, TIFF and some other image types) which comes together with a world file. The world file contains geographical information on how to place the image on the map.
Maperitive only supports non-rotated georeferenced images. Basically, only images that are compatibile with the Mercator or Equirectangular projections can be used, since Maperitive currently does not offer any kind of image rectification mechanism to convert the image from another projection. Rotation information will be ignored when loading the image and the image will probably not be properly placed on the map.
export-bitmap generates two other types of the so called "sidecar" files:
GeoTIFF file is an advanced form of a georeferenced image. It can contain a lot more information compared to world files. Unfortunately Maperitive is currently not able to read or write this georeferencing data in GeoTIFFs.
There are tools which can generate world files from GeoTIFF information. Again, same restrictions about the map projections still apply.
My hope is to be able to add both image rectification and GeoTIFF capabilities to Maperitive in the future. Unfortunately .NET is poorly equipped for such a task, so implementing this capability will require a lot of work.