Maybe seeing one i have only just started may be of more use Mr Nemo
![Image](http://homepages.tesco.net/sculptor/horse.jpg)
in a paint program smooth gradients will curve objects out (horses head and neck)
Then i use a lighten brush or a darken brush to pull things forward or push them back.
Gaussian blurs for smoothing etc etc
So in essence its the same as using curvy maps.
Simply keep in your mind --- is this part of the horse closer or further away than another part ?
If it is closer its got to be lighter.
Black backgrounds will make freestanding objects.
You probably want to save the image at some early stage to use as a final texture because the best depth map will probably not make the best texture.