Hi,
Question on removing backgrounds on a portrait so "only the photo engraves and not the background"

I know this topic has been discussed before, but I can't seem to get it to work. I'm trying to engrave a portrait onto marble. But I can't seem to remove the background of the photo so that a close up of the subjects head will be the only part to engrave. I'm using photo paint and then processing in photograv. When I engrave the photo, the removed background still engraves.

Can anyone help break down how to remove the backgrounds on a photo.

Thanks
ron