Use the add tab then select Image Overlay in Google Earth to add the JPG overlay. In the dialog box add the name of the overlay, provide the path for the JPG overlay and adjust the transparency of the overlay.
It can be a bit tricky positioning the overlay in Google Earth. However, with the route displayed in Google Earth from part 3: Add Route to Google Earth, it is a simple task to match up the route with Google Earth and the overlay by using the green marks to adjust the corner, edges, center and rotation. It may also be necessary to adjust the transparency (in the New Image Overlay dialog) to a level that allows adequate viewing of the JPG and imagery beneath.
Once you are satisfied with the alignment of the source material, select “OK” on the New Image Overlay dialog box.