To do a 3D engrave of that piece is a fairly advanced project since you would need a 3D scan (your Glowforge will not do that) or at least a photo taken with very even lighting. What you would want to do is generate a depth map (search this forum for depth map, you’ll get a few hits) that creates the correct black to white graduated image that Ekla refers to. I could be wrong, but I don’t think you’d get a good depth map from that image, there’s too much side lighting.
While you’re reading up on depth maps, you might want to concentrate on getting a good quality regular (2D) engrave of the image. There’s tons of advice on the forum about optimizing an image for photo engrave, but basically you want to convert it to greyscale and bump up the contrast in GIMP or Photoshop. I would also erase the background to either transparent or pure white and erase that pin that runs along the back side of the piece. That should get you a decent 2D engrave.