Try a company that does laser engraving for plaques, trophies, etc. They can scan in a photo and reproduce it on a piece of wood, veneer, or directly onto the riser. You'd be amazed at what they can do.
I was asked recently to make a commemorative plaque for a manager at work and because the timeline was too tight, we took it into a nearby place and had it laser engraved. Did it ever pop!
Dave.