Did you render at the same aspect ratio as your preview? And when you imported the background and Poser asked if it should resize the window to fit, what did you answer? Poser 5? I think I remember a problem with Poser 5 and background images, but I'm not sure if a cure was found...

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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.