The client provided an image for this project, but it’s wasn’t quite suitable as-is. To change it into something that would look pleasing engraved, I set up a few adjustment layers in photoshop in the following way:
I first added Black & White and Posterize Adjustment Layers. Then, fiddling with color sliders in the Black and White adjustment makes it easy to fine-tune what gets engraved and how darkly. (The default setting for Posterize of four levels works out great with plywood and my Glowforge laser.)
Results
I made a half-scale version first to verify the look-and-feel with the client. 
Finished product next the the half-scale version. 
Big Jakes all the way down.