The selected image is scanned from left to right and the light is converted to sound.
Light near the bottom of the image produces low notes and light near the top of the image produces higher notes.
Brighter light produces louder sounds.

Keyboard commands:

alt + p : play/pause
alt + left/right arrow : slower/faster
alt + l : toggle loop mode
alt + b : make brighter
alt + v : make darker
alt + c : increase contrast
alt + x : decrease contrast
alt + i : invert brightness
alt + h : open/close this panel

For the best results, try lowering the brightness and increases the contrast slightly.