Confused about getting Open CV on Beagle board

Hi ,

I got BB rev C working with angstrom image is fine.My goal is to run
Open CV on beagle board.

How can I build the the Image(including Open CV).
Can I use the Narcissus online image builder or should I use the
Bitbake, OE to get the image.
I have seen some posts they are compiling open CV on beagle board it
How can I do that,Please kindly suggest me.

Thank you,