Before we get to HOW to create Gray Scale images for 3D laser low relief carvig - here are some examples that were created in PhotoShop - to give you some ideas for YOUR images.

And here are some ideas created in a simple 2D CAD program called Aldus SuperPaint 3.5 - last version was from 1993! The patterns were pasted into PhotoShop and saved as both JPEG and GIF file format files. The lasered low relief "carving" are on the right (maple and honey locust)