With all the discussion lately of using software and photos I thought I would share this idea....
You probably have heard of "rapid prototyping" where you make fast, sometimes crude, models of some item to test some design aspect.
I like to use digital pics to do this for modeling ideas. If you have two or more photos of different elements, taken from roughly the same perspective, that you would like to include in your concept, sometimes you can use photo software to create rapid prototype "photos" to test a modeling idea.
For example I am brain storming a diorama concept that would be the result of a kitbash of a commercial kit and a scratch built portion of another structure I saw on another layout. Using graphics software (I like Macromedia's Fireworks) and a couple photos I can create digital mock ups to see if the idea is even remotely feasible....
While not perfect, it does allow me to see if the concept is worth spending more time on. This photo only took me a couple minutes to put together.