Making this low priority, for next year maybe.

From Pekka Sarkola:

"""
I think best term for this request is "Georeferenced image files (PNG, PDF)".
 
I presume there is not standard way to include coordinates inside PNG-files. World files are common way to georefence raster files. Here is few links:

    * http://mapserver.org/input/raster.html#georeference-with-world-files
    * http://webhelp.esri.com/arcgisdesktop/9.3/index.cfm?TopicName=World_files_for_raster_datasets

I think also Map Projection information will be valuable. If you can also add projection file with your map produtcs, that will also very valuable. This reference is for shapefiles, but I presume it works also with raster files:

    * http://en.wikipedia.org/wiki/Shapefile

BTW, also following information should be on the maps (IMHO):

    * Map projection: this information should be also on the map
    * WGS 84 / MGRS coordinates grids: maybe there is some use of these also. At least if you are using GPS devices to collect information / navigate
    * Georeferenced PDF: I'm not sure if you tools support these. But it will very convient, if PDFs will be georeferenced and layered. This can be very big job.
"""

A reference on World Files:
  http://www.gdal.org/frmt_various.html#WLD
World File information can be included into a PNG file:
  http://www.gdal.org/frmt_various.html#PNG

Suffix for PNG + World File is .pngw or .pnw.

Another reference: http://www.cadforum.cz/cadforum_en/qaID.asp?tip=3515

From Pekka Sarkola:

I really need coordinates inside of PNG or GeoTIFF files. With PNG this should be world file (or similar), GeoTIFF should be better solution. With this feature I can take picture inside of my GIS tool (MapInfo, ESRI ArcView, uDIG...) and attach my own GIS layer top of your maps.

My question: how to encode such coordinates? Any standard?