Using SIFT for Augmented Reality

Question

I\'ve come across MANY AR libraries/SDKs/APIs, all of them are marker-based, until I found this video, from the description and the comments, it looks like he\'s using SIFT

Answer 1

As always, Wikipedia is a good place to start from : http://en.wikipedia.org/wiki/Scale-invariant_feature_transform, but note that SIFT is patented.