Compared to other optical flow projects on Youtube, this sample image is just child-play. This link can inspire you more, my friend Optical Flow Exercise.

So what have I been doing?
I put together what looks like an approaching stop sign. The vectorMap (middle) is generated by a combination of GoodFeatureToTrack, FindCornerSubPix and CalcOpticalFlowLK. Refer to the OpenCV Documentation manual and the OpenCV Book if you’d love to get started with optical flow. Find me on facebook if you want to track down the source code / need help write your own : )

further inspirations:
get good frame rate with FPGA.
dense optical flow (this is spare optical flow)