My last render:
http://jayhawker.deviantart.com/art/Realistic-Abstraction-159654616This was interesting to make. The cloud layer was blended by an image mask made on Apophysis and edited on Photoshop.
There was a problem, however, that I didn't know how to fix:
Initially the cloud covered the whole sky, with high density, and depth.
Then I used the Image Map Shader with Projection Type = Through Camera.
Everything was fine until I create the terrain. The bottom part of the cloud created shadows on the terrain, even the terrain being in front of it.
After few minutes trying lot of things, I've decided to create another camera on the same position of the one I was using and change the Projection camera of the Image Map Shader to this new one. Worked fine and cloud (and its shadows) went to behind the terrain.
So, this is a tip for everyone who may get the same problem: use two cameras

Hope you like the image.
And be welcome to watch me on deviantArt