MAPC2MAPC will convert almost any calibrated map for ttMaps - or you can calibrate a scanned or downloaded image. You can also use Mobile Atlas Creator to make a OZI MAP and PNG from various on-line sources then open the MAP calibration file with MAPC2MAPC.

Before you start, you need to install GDAL. Download and install GDAL and the ECW plugin Then start MAPC2MAPC and use Edit>Locate.GDAL_Translate to open the GDAL_Translate.exe that you have just installed.

Use File>Load Calibrated Map then File>Write ECW. Then copy the ECW file to the TomTom and install as described here. If you have a large number of maps, then they can be processed with Batchbuilder

If the original projection is Mercator or Spherical (Web) Mercator then the ECW is the same; otherwise the map is reprojected to Latitude/Longitude  (Plate Carree) - this will still be positionally accurate but the map may have been rotated and there may be some white padding introduced along the edges.