What algorithms can you recommend for marker tracking in augmented reality?

Question

augmented reality

Played around with Vuforia. It works really well, but there are some points that confuse (price, work and service in general)
And now if you write it yourself. In general, the search for closed contours is understandable. Vuforia, on the other hand, builds a certain cloud of control points in advance, and then looks for this cloud in the picture.
And now it’s not clear to me how the cloud of control points in the perspective from the photo is firstly selected, and secondly compared with the cloud of marker points. Compared to different marker angles? What are the algorithms for finding the similarity of such arrays?

Answer 1

SIFT/RANSAC
, or just Hoare's cascades, if the marker is a special picture.

Answer 2

Alex Brush R.O.B.