Stero channels aren't encoded in the depth and radial axes. They're encoded in the same plane, but rotated 45 degrees, so a mono record player (depth only) plays a balanced sum of each channel.
Edit: mono is radial only, not depth.
Edit: mono is radial only, not depth.
Following this animation I'm left thinking that you could do a bit of filtering to better extract the wave(s) from an image, though you'd require a particular setup for the lighting conditions to get the best possible quality out of it. And then back to my first idea: probably a laser-tip would be the best tool here too.
Unfortunately I don't have vinyl records around to test any of this!
You mean horizontal only?
Old Edison disc records encoded single-channel audio in the vertical axis (varying the depth), but regular 78s and single-channel vinyl records encode the audio in the horizontal axis.