[Nibbles]

This is something I have considered too (with mice, webcams, OpenCV, then various vision algorithms), but soon realized it was impractical because of the limitation of speed. Especially for mouse cameras, the resolution and (fast compared to standard video) framerate is too low for anything more then a foot per second (if you are lucky). Going back a generation of mice and using a ball/wheel with optical encoders is your best bet, and probably for the next few years. This years floor also poses a problem, there may not be enough contrast of the texture to track.
<ins>Wait, the floor is textured, so a good camera would be able to keep a lock on the floor texture with proper lighting. If you had a camera that could do the job.</ins>