Conversion of KML format to JPEG picture format basically represents export of rendered version of the data from .kml file to a raster picture (.jpg). For this you will need a program that can fetch and view Google's KML format and export the output as picture, for example GPSMapEdit.
Some users also simply open .kml file using a web browser and screenshot the output to produce the picture. Not very elegant solution, but works as well.
Updated: December 9, 2016