Poser has a built-in shadow catcher material capability but my shadow catcher is more powerful. You can calibrate it using your lights so it can exactly reproduce the shadowing found in the environment. Poser's won't do that.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)