Well, this is a quite simple method.
With TG2 open, click on the Objects tab. There, you will see an object called "Background".
Click, and inside it, you'll see a tab called "Surface Shaders". Click on it.
There will be a default shader called "Background Shader". You will create a new shader to take the place of background shader, and it will be an Image Map Shader
To do this, click on the rightside "+" button, and goto Create New Shader, then Colour Shader
In Colour Shader menu, click Image Map Shader
Then, you will be asked to choose any image from your computer. After choosen click the "+" button again and click "Go To Image Map Shader 01"
The example3 window will appear.
Set the projection camera to Render Camera. This setting will make the image to be always directly in front of the camera named "Render Camera", but you can choose any other camera to project it. And also, it will need to be lightened to appear well, so I put the main sunlight opposite to the image projected (directly behind the camera, at a negative elevation, in this case) and created another sunlight to lit the terrain a little.
All the images I've used in this and other renders are property of their creators.
Hope it helped!!
