ROOT and SIFT are patented, that's why ORB was developed for OpenCV. It's mentioned in the OpenCV tutorials: http://docs.opencv.org/master/db/d27/tutorial_py_ta

ROOT and SIFT are patented, that's why ORB was developed for OpenCV. It's mentioned in the OpenCV tutorials: http://docs.opencv.org/master/db/d27/tutorial_py_table_of_contents_feature2d.html http://docs.opencv.org/master/db/d27/tutorial_py_table_of_co...