I am by no means an expert at this, on the contrary, I am mere novice. I stumbled around in Photoshop Elements 2 to produce this and I'm not too sure of the results. The first problem that I have is I usually photograph my models against scenic backgrounds instead of using a neutral color backdrop, which makes selecting the diorama from the background in Photoshop more difficult., so shoot your models against a neutral or black background and save yourself this headache. After selecting the vehicle, building and groundwork using the various selection tools, (especially the magic wand) and editing out the background of the model photo, it's simply cut and paste the model photo onto a new background image. Then use Free Transform to scale the model photo against the new background. Touch-up tools like clone, smudge and painting tools can fix editting errors. You want to use images that are close to the same file size, in order for them to be editted together correctly. This is about all I know. I have the manual, but I haven't really read it yet. There are tutorials available online too.