I do something similar, but in a 3D manner, a sort of peak book that
accordians forward with a distinct foreground, midground and background. I
have them bring in reference materials, i.e. 3-5 pictures of clouds,
mountains, skies, etc, and keep a file, so that when they are about to do
their landscape, again they "make a frankenlandscape" a combination of many
photographs. They do NOT wholesale lift, but use as reference material from
their file of trees, mountains, skies, clouds, lakes, grasses, etc.
Again, while I prefer students to work from observation as a first choice,
sometimes that is not possible. It IS possible to work from their own photos
(as we can assume they made the aesthetic decisions on their own when taking
the shot).