Hi Brian,

That way of doing displacement map is not good at all and you will just have something that more less look like the original details.
To capture the details you need to generate a 16 bits (at least) grayscale image of the elevation, and it's something different than screengrab a top lighted model.

A normal map will give you a much better result too, but also requiere using some extra tools, like xnormal
http://www.xnormal.net/2.aspx

Cheers