To start this topic off, I want say that I am very impressed how the Shapeoko 2 performs when laser engraving photos, especially with the J-TechPhotonics laser system.
We are using the J-Tech grbl that can run X,Y & Z spindle code or X,Y & S PWM laser code and outputs on Pin 11 for the modulation. It can be downloaded here.
This photo engraving was done on our Shapeoko 2 with the 2.8W J-Tech Shapeoko kit and the g-code was generated with PicEngrave Pro 5. I used PicSender to stream the 1,065,369 lines of code in the file to the Arduino UNO.