OpenCV needs a number of third-party libraries to operate. For example, opencv_highgui works on GTK, which in turn works on glib (among many others), and so on. I am far from knowing all the dependencies, but the good news is that, to my knowledge, other than SURF and SIFT (as you mentioned) are not limited in the commercial use of all things opencv, and there is no need for license. OpenCV 5 will be released soon. It will be a great publication to celebrate the 20th anniversary of the OpenCV! In addition to many new features and improvements, the OpenCV 5.0 (and in the OpenCV 5.x series) will bring as better optimization for different architectures, support for new deep learning topologies, improved 3D vision algorithms, etc., is the other important change that has been discussed for some time and that we will finally do, the openCV migration from the 3-BSD-BSD clause to the Apache 2 license. OpenCV software contains code written by third parties. This software has its own individual license or copyright. The following links refer to the license or copyright associated with the third-party software used by OpenCV. OpenCV 4.4.0 and lower versions, including OpenCV 3.x, OpenCV 2.x and OpenCV 1.x, are licensed BSD 3-Clause. In May 2016, Intel signed an agreement to acquire Itseez from a leading developer of the OpenCV.  In principle, nothing should change, business as usual, but with additional protection against patent applications. OpenCV under the Apache 2 license could continue to be freely used for commercial and non-commercial projects. If you have any questions or comments, please ask them below, or in the corresponding post in our release tracker here.
By downloading, copying, installing or using the software, you accept this license. If you do not accept this license, do not download, install, copy or use the software. BSD is a good license that has been used in OpenCV from the beginning. It allows people to use the library in any type of project, be it education, research, personal project or up to a commercial product, without restrictions. By 2020, however, it may not be quite sufficient for the current state of the computer field of view, which has grown rapidly over the past 2 decades (in part, thanks to OpenCV). In particular, BSD says nothing about patents, which means that the code under a BSD license may contain implementations of certain patented algorithms, and the code itself is “free,” but it is not free because patent holders can ask users of that software to concede the patents contained. Today, Computer Vision is patenting more and more algorithms ranging from traditional vision algorithms to deep learning topologies and hybrid approaches. We thought about possible solutions, and we discovered that Apache 2 was the easiest way to tackle this problem.
Apache 2 is newer than BSD and contains not only the same characteristics of BSD licenses, but also special patent clauses.