With some experimentation, it turns out that adjusting the following parameters are useful:

• - command-line thresholds: increasing the range reduces the noises as seen from the 'Diff window'
• - perimeter ratio argument to cvSegmentFGMask(): reducing this to keep smaller area from being thrown away. It works well if the noise has been reduced.

Now able to put the 'car theives' on the 'Connected' screen after tuning the above arguments.

Notes: a car leaving the parking lot would leave a permanent 'change'. The passing-by cars leaves mark also. The rays from headlight introduced a big block of 'differences'. Low frame-rate makes fast-moving object blurry. The person is more likely to show up in the 'radar' if he/she wears light-colored clothes. Skin is 'dark'.

The number-of-frames to learn MATTERS: use small value if the expected movement is small, like the tennis lesson videos. Otherwise, all the subsequent movements will still be 'in the dark'.

Finally, having trouble with editing SVN log message. Needs to setup the pre-commit hook. The template that comes with SVN installation are Unix shell scripts. Able to found a great working one here for Windows (Awesome!):
http://ayria.livejournal.com/33438.html