Inserting raster images. Where to start?

I'm in the process of creating a 3D of a building which I intend to render. What I don't understand is how do you create the final result with the raster images of trees, people and cars etc. The following link gives an example of what I'm tring to achieve. http://www.carlgoodman.co.uk/architectural/architectural-4.html

Can they be added in autocad or are they added in photoshop?

i dont think raster image is what you want. I use that to lay down a jpeg to trace.

There should be environment settings where you can use an image(ive never done this in acad). hopefully someone will chime in

You might want to check out RPC's (Rich Photorealistic Content). There is a company called Archvision that makes these.