hi,
maybe this is not exactly what you want but it might show you how to do it (and how fast it can get).
we ported a library called ARToolKit to the PocketPC some time ago and optimized it by using fixed point math, lookup tables, etc. ARToolKit finds rectangular "markers" in camera images and calculates the cameras relative pose from it.
our version runs at up to 150 images/sec on a PocketPC and since you probably don't need the pose estimation part (which is a major bottleneck) it could run a lot faster in your case...
you can find more information and our complete source code at
bye,
Daniel