There's a method that uses 4 photos with controled lighting to produce
a normal map after a fair amount of editing. This normal map can then
be processed by a utility to produce a heightfield.

Details about this method can be found at Ryan Clark's site.
http://66.70.170.53/Ryan/heightmap/heightmap.html
This method produces normal maps that have no blue channel data.

"In the most common implementation of normal maps, used by Valve's
Source engine and implemented in hardware in nVidia cards,
the red channel should be the relief of the material when lit from the 
right,
the green channel  should be the relief of the material when lit from below,
and the blue channel should be the relief of the material when lit from
the front" -- Wikipedia. This is not to be confused with a POVray
normal_map, or bump_map.

Instructions for editing the images are provided for Corel PSP 10+.

Inputing the resulting normal map into Ryan Clark's Displacement Map
Creator software can make a greyscale height field image, at 512 x 512
only. It promps for ATI style, I think inverting the output.

The image can be fed into POVray, or used to correct the blue channel
of the normal map (for game engines). It seems to handle sharp
horizontal edges near the top and bottom poorly. Don't forget to make
sure your photos line up, use the perspective tool and resizing.

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