Ah. I don’t know how I missed that in the first post. Plywood isn’t the best choice for 3D engraving. You want to use hardwood for that. Half-toning works for photographs into plywood, but you’ll still want relatively high contrast images for it to work very well.
My first test of grayscale engraving was with a Goudy Initialen letter (free version of Goudy Cloister Initials, the original version of which was published in 1908). I’d used them for a 3D printing project and for that I wanted three depths. It turned out for making my leather stamp, monochrome worked better, but I did some tests on Proofgrade Maple Hardwood:
In the photo, the one on the left is halftoned and the one on the right is vary power.
Aside: I’d decided to use Goudy Cloister to customize one of the catalog projects thinking I’d add something original, but of course @jules beat me to it and Discourse showed me that old thread as a “recommended” one at the bottom of some other thread I was reading. It probably noticed I’d been poking around looking at the font again via Google. The internet, it’s stalking me.