A posture-correcting chair that begins to tilt in the direction you are hunching until you either straighten your posture or fall over.
Develop a subconscious habit of keeping your posture straight.
You either sit correctly, or you can't sit at all.
Any type of chair can be clamped onto a motorized platform. The platform has to be wide and heavy enough so that it doesn't tip regardless of what happens in the chair.
The platform strongly grips the chair by the central leg. From then on, It can tilt the chair up to 90 degrees in any direction.
When bad posture is detected, the chair gives you a few seconds to correct it before slowly beginning to tilt the entire chair in the direction your posture is leaning. If you correct your posture, the chair goes back to being upright. If you don't the chair continues to tilt until you tip over. The chair stops at 90 degrees and remains there until you get out of it. Then it moves back to upright position.
Posture recognition software
There is probably a simpler way of going about it, but for the moment I can think of this:
One camera is placed in front of the person (on the desk, under/above the screen, etc), the other is placed on the side.
The initialization process asks the person to sit perfectly upright in a way that is comfortable for them. They confirm the perfect posture by clicking on a button. The process is repeated a few times throughout the day so that the software learns what normal/ideal conditions are for each individual.
From then on, if the person tilts their head, shoulders or spine in one direction and keeps it there for more than several seconds, the chair begins to tilt in that direction. The only way to stop/reset the process is to sit upright again.