It is very likely that they were created by Yen Sid.
From the outside, they resemble old-fashioned projector screens constantly showing the opening credits of a cartoon made in the Who framed Roger Rabbit ? world about a past event of the Disney war. But as they are magical, people can jump in it, an then muse in a 3D projection of the cartoon in question. In them, it is possible to see past version of various characters, often doing over and over again what they were doing in the movie that is the base for this subworld; however, despite them being only projections of what their originals were at one precise moment they were filmed, they appear — by the vertue of Yen Sid's magic — to have their own existence, as if a traveler speak to them they will react. Some Friends were filmed and their filmed counterparts can be seen inside these hubworlds, such as Peg Leg Pete and even Chernabog himself.