Shortly after I started this project, I dug through my CD collection to pull out some of the Moody Blues albums so I could easily reference the liner notes if I need to. Looking at the cover of On the Threshold of a Dream, I discovered that there are some elements from the songs in the art work:
There might be others that I'm missing, but off-hand I noticed three. In the top center, there's "the white eagle of the North flying overhead" from "The Dream." From "Are You Sitting Comfortably," there's "a fleet of golden galleons" in the lower left hand corner and "Merlin cast[ing] his spell" on the right. Because there are these two references to "Are You Sitting Comfortably," it would seem that the castle-like building in the upper left hand corner is meant to be Camelot, which is also mentioned in the song.