Backwards, yes.  My thought was to position the camera, log the world to screen postions of the vertices, click to select a vertex based on screen coords.  Refresh the world to screen list when the camera has moved and stopped moving again.  The clicked mouse coordinates would have to be checked against the logged list values to find the closest match.  Not the way it should be done, but, once again, this is yet another PoserPython function which stops somewhere short of being immediately and fully useful....  Sigh.

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Cage can be an opinionated jerk who posts without thinking.  He apologizes for this.  He's honestly not trying to be a turkeyhead.

Cage had some freebies, compatible with Poser 11 and below.  His Python scripts were saved at archive.org, along with the rest of the Morphography site, where they were hosted.