This article is from the Disney's Haunted Mansion FAQ, by Don Bertino email@example.com with numerous contributions by others.
The busts are actually inverted. Like they actually took a mold of a
bust, made a thin material that lets light thru.
They sold under the name Living Image. I have only found the small one
(the box being 4 x 5 inches and the bust being 1"x1 1/2". There is a
small mirror in front near the bottom that you need to use to reflect as
much light as you can on the face. There is a male face (Lincoln's) and
a female face (??).
They sell for $7.99 and can be shipped. Their address is:
(A division of Spencer)
Downtown Plaza #919
545 Downtown Plaza
Sacramento, CA 95814
They sell this effect in the Toontown Gag Factory around Halloween.