This is the resort we stayed at. I had a hard time finding this as the resort is long gone. Looking at the sunset photos in the album, told me that the resort had to be on the western side of an island. Looking at the Google Map of the Belgrade Lakes points to Hoyt Island on Grand Pond as a possible location.

A search led me to the 1949 edition of "Maine Invites You", which had this ad. The 1952 edition listed the cabin rate as $7.00 per day (!!!!) When I saw the name, R.E. Boomer, I knew this was it!