OK so I had some time to look into this, implementing the changes recomended, didn't help unfortunately.  This may be a result of the plane primitive not having any y depth (seems plausible).  To recap, the problem generally works like this:

1.  Create an image in photoshop of several squares overlapping each other (make sure each square is a diffrent shade of solid grayscale, e.g dark-grey, medium-grey, light-grey,...etc.

2.  Save the image as a bitmap (.bmp) file

2.  Launch poser and load the flat, single-sided primitive (from props->primitives-single-sided plane)

3.  Go to the default material for the one-sided primitive and connect a 2d image node to the displacement attribute.  Specify the bitmap you just created.  Set displacement attribute to .08

4. Create a 640x480, 300 frame animation of the main camera trucking in towards the flat plane from the side or a 45 degree angle so as to be able to see the y angle of the render (e.g. keyframe 0: flat plane fills half of the screen, keyframe 300: flat plane fills 3/4 of the screen)

5.  Render using firefly with displacement enabled

Result: Displacement height is correct, however the sides of the object display odd shading artifacts over time.