Do you want to share your secret? I am in my first week of laser ownership and am trying to learn PhotoGrav. I want to perfect photo engraving so I can get the "wow" factor.
You'll find lots of great answers regarding this topic if you perform a Search in this forum.
Don't be intimidated. It's the 3rd link on the left below the EE logo and results arrive fairly fast. Suggested search terms to start with could be photo, granite, marble, photograv to start with and select "from the beginning of time" for your search dates.
You'll be happy and well-educated with the results you find.