Actually I used the terragen image in poser as a background and rendered on top of it. It never gives me shadows, I have tried all the settings. Shadows is something I usually add in PSP or Photoshop. This image is still unfinished, it will probably take me a month to get it all right
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I think u must add a ground to get shadows [link] This is a link to a plugin for terragen, u hav to export the terrain into *.obj and import it in poser.
I hope this will help u coz it's difficult to do a realistic shadow in psp or PS.