Carving of a Picture

[drandals]

I am trying something I've never do before. Trying to take a picture and carve the image. I have used the smoothing option, but is there a way to reverse the depths. Example, the nose in instead of out, eyes out instead of in. I'm sure its simple and I am overlooking or where can I see a tutorial on it? Thanks

[Rcnewcomb]

Look at the Trout tutorial under 3D modeling.

[Pete Cyr]

select combine mode of subtract