You should have received this DBoW2 version along with ORB-SLAM2 (https://github.com/raulmur/ORB_SLAM2).
See the original DBoW2 library at: https://github.com/dorian3d/DBoW2
All files included in this version are BSD, see LICENSE.txt

We also use Random.h, Random.cpp, Timestamp.pp and Timestamp.h from DLib/DUtils.
See the original DLib library at: https://github.com/dorian3d/DLib
All files included in this version are BSD, see LICENSE.txt