Fuse in the camera

[Summertime]

Much like laser mice, using the camera with a super low resolution and high framerate might be worthwhile

Flashlight would have to be used, and it wouldn't work great depending on distance between camera and flashlight, but it could help reduce drift, even if its delayed information.

[LinuxinaBit]

I was thinking something like this could at least help with positioning, but it would be a bit hard to work with as phone cameras don’t update that fast even when compared to cheap office mice.
There would also be focus issues, but I’m sure that could be somehow worked out.
More on how this could be implemented:
https://en.wikipedia.org/wiki/Optical_mouse#Principle_of_operation
I believe it would be easier and much more effective to simply implement #8 first.

[VirtCode]

I've previously thought of this too, but also think that this would quite difficult to achieve, especially as the usability of the data probably strongly depends on the hardware configuration. But thanks for the suggestion! I might consider looking at something like this after having implemented things like #14, as I think that the IMU-based positioning still has quite some room to improve.