Last night I loaded up a poser scene that had an 800x800 background attached as a base for a new scene.  So I switched backgrounds to a 1000x800 one and resized the preview and render dimensions.  However when I went to render, the background ended up rendering at 800x800, it had that generic tan color to the sides, despite being 1000x800.  I couldn't do anything to get the background to render correctly so I ended up importing a primitive square and using that as a BG.

However is there any way to correct the background problem when I run into it again?

Did you go into the menu and change your render dimensions?

If you plug the image node into the Alternate_Diffuse channel on the PoserSurface, it will be self-lit and will not react to any scene lighting. You can adjust its brightness using a greyscale shade in the Alternate_Diffuse colour.

To see the image in Preview, plug the image node also into the Diffuse_Colour channel, but set the Diffuse_Value to zero.

(edit) there are no scene lights in the above render - both the square and my environment-sphere gradient shader behind it are self-lit.

OOPS. I forgot to set the Specular_Value to zero!

Anybody ever wonder what the Image_Map Auto_Fit property does? Anybody?

Quote - Anybody ever wonder what the Image_Map Auto_Fit property does? Anybody?

Well, it appears to be maintaining the source image's aspect ratio and adjusting the size to fill one dimension of the square's surface.
The colour of the unused area depends on the Image_Mapping and Background_Color, but Image_Mapping = Alpha does not do what I would expect (make it transparent).

Isao, I used the ambient color instead of specular and that worked well enough.  I'll try your method next time though.

I just retried the image and BIll's suggestion worked.  I thought about using it but I decided against it because the image map and the render were both the same size.  I didn't think poser would try to resize the image map.

Here's a final version of the image.  If you check it out in my gallery I've included a youtube link to the song that inspired it.

Sweet picture.

No need to try the alternate channel - ambient does the same thing in this case, and it gives you a dial instead of a colour to adjust brightness.
But can I see soft shadow on the background from the figure? Or is that just a darker area in the background image?

I think that's the background... I left the bottom left darker on purpose because the song I based the image on talked about morning light.  So I was going for a morning twilight look.

Quote - Anybody ever wonder what the Image_Map Auto_Fit property does? Anybody?

I have wondered when you are going to change your avatar :)