For optimum bump-mapping, consider using a different map depending on the closeness of the object being rendered. For a person, in poser, a different map should be used for close-up and distant renders. If you notice little effect from gray-to-gray in your bump-maps, increase the contrast in the bump map to bring out the bumps more. Bump maps are also pixel averaged, like textures, so their effect is often diminished at long distances.