You could detect angles and lines using for example Hough transform (http://galfar.vevb.net/wp/2011/deskewing-scanned-documents/).

Has the example page moved somewhere?

It says PAGE NOT FOUND!  :o

Hey Guys!
I've been try out this lib and I'm wonder how possible it would be to detect angles and to draw lines on a image containing a couch or a table so that I can color each of its faces a deferent color ?

example :http://www.mathworks.com/products/image/demos.htmlfile=/products/demos/shipping/images/ipexangle.html

Thanks :)