How to burn flat images in wood?

Has anyone ever added a wood burning type tool to a cnc router? I mean
like a torch or something. I know the best way to burn a flat image
into wood would be to use a CO2 laser, but that is very expensive.
There must be an alternative to expensive lasers.
I see allot of software for making images in wood like ImageCarve,
DeskArt, or ArtCam. But those are pretty much 3D relief. I was
thinking more of just a flat burned image like a CO2 laser can do.
Any ideas?