Not a photoshop, not an illusion:

This photo looks like two images stitched together; above is a normal forest, and below, a strange, Martian one. But it's a single image from a single place and time — the hills of western Hungary, six months after a devastating industrial accident.
Story:
http://www.npr.org/blogs/pictureshow/2012/07/14/156778569/this-is-not-a-composite-photo#