I see a lot of questions asking about strange effects when you render, I think a lot of the problem is people are using the Square prop instead of the One Sided Square prop. Here is an example, One Sided Square on the left, Square on the right.

However this is fixable by adding a tiny amount of displacement to the texture in the material room and clicking Use displacement maps in the render settings. Again One Sided Square on the left, Square on the right.

This problem has been known for quite a while, poser 5 and 6 "don`t like" double sided polygons.

Yes, but it keeps popping up all the time here in the forum. So obviously a lot of people don't know about it. I was just talking to someone about it in another thread. This should probably go in the FAQ or something.

However this is fixable by adding a tiny amount of
displacement to the texture in the material room

There is a render option "remove backfacing polygons" which can be used instead.
By the way, are these black spots some kind of secret message from Mars? Or from the Firefly renderer ...

In Poser 6 SR1, you can use either square. Just make sure that you check "normals_forward" for it's material.

Ok. I admit it: I'm a nerd. That pattern looks very similar to the "Aztec" patterns on Enterprise starships.

Thanks for the tip, stewer, I had an animal ear prop I made and I kept getting an odd black area on the inner part of the ear. I kind of suspected it was due to a normals problem, so I checked normals forward on the ears and the black area went away.