Actually Ockham made a python script for just that. It is most likely in Free Stuff. It checks for any RSR that has a corresponding ong and then delete the rsr if it finds the png :o) Very handy. And P5 does Phyton just fine :o)

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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.