Our friends in the map library at Brock University in St. Catherines, Ontario have put together a very nice how-to on creating super overlays for Google Earth using Geographic Imager and Adobe Photoshop.
These instructions describe the process of georeferencing a high-resolution image, creating a geotiff file, using Google Earth Pro to make a super overlay and how to provide access to others. The full process is outlined here https://www.brocku.ca/maplibrary/Instruction/Creating_a_super_overlay.pdf
The Brock University Map Library can be contacted at maplib@brocku.ca