Hm I seem to remember this as a known issue in Poser 7 (hope that's what you use...)

The solution is to Render over Current shader, then plug the picture in as a Image Map there.

That also helps on the white border issue,

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You just can't put the words "Poserites" and "happy" in the same sentence - didn't you know that? LaurieA
  Using Poser since 2002. Currently at Version 11.1 - Win 10.