[GuiA]

It depends - tracking a white piece of paper on a snowy backdrop is definitely a hard challenge ;)

But all in all, I wouldn't say it is. In undergrad the final project of my computer vision class was to track a soccer ball over video frames. White circular object against mostly green backdrop- fairly straightforward.

[m_ke]

I'm pretty sure what Meron meant was getting the orientation of walls so that they can project stuff on top of them.