Final Project for CS 445, Computational Photography, at the University of Illinois.
Presentation slides and a demonstration video available at [web.engr.illinois.edu/~mrmillr3/final].
Aided by a mobile phone's orientation sensors, find the perspective transformation between the current frame and a user-selected keyframe at a real-time rate (~30Hz). Then, using this transformation, reproject a user-drawn rectangle after the user rotates the mobile phone, and have the rectangle "stay in place" relative to the outside world.
I'm very happy to take questions. Email me at mrmillr3 {at} illinois {dot} edu.