OK, was able to whip up a quick and low resolution test to show whats going on. Its just a trick of perspective really.
See the images below and the attached .tgd
The "base image" is a photograph I took. Notice how I aligned the horizon in TG2 to the horizon in the photo by simply moving the camera around. As stated, the results in this example are low resolution...simply use a high resolution photo to increase detail. You can even add displacements with different textures, etc, which is what I did on Sand Castles.