I would reccommmend doing this carving in iether lexan or corian.
use 1/4 inch and if using lexan you only need to go .07 deep making sure you scath all of the top
if using corian you will want to go deeper so the light can ome thru and make it look like a black and white pic.
as far as the image goes itself when you bring it into designer bring the height down til all the high peaks are gone.
if you are not getting enough control that way bring it into coral or photoshop and change some of the black to deep grey or white to soft gey this will bring the greyscale closer and therefor less contrast when carving.
good luck
Tim
I know there is no point in reinventing the wheel, but reinventing myself is a worthy goal to be sure.
Tim