opencv : https://github.com/opencv/opencv?tab=Apache-2.0-1-ov-file#readme
libpng : https://github.com/pnggroup/libpng
PNG Reference Library License version 2
Copyright (c) 1995-2018 The PNG Reference Library Authors.
Copyright (c) 2018 Cosmin Truta.
Copyright (c) 2000-2002, 2004, 2006-2018 Glenn Randers-Pehrson.
Copyright (c) 1996-1997 Andreas Dilger.
Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc.
The software is supplied "as is", without warranty of any kind, express or implied, including, without limitation, the warranties of merchantability, fitness for a particular purpose, title, and non-infringement. In no event shall the Copyright owners, or anyone distributing the software, be liable for any damages or other liability, whether in contract, tort or otherwise, arising from, out of, or in connection with the software, or the use or other dealings in the software, even if advised of the possibility of such damage.
Permission is hereby granted to use, copy, modify, and distribute this software, or portions hereof, for any purpose, without fee, subject to the following restrictions:
zlib : https://github.com/madler/zlib
zlib License
Copyright (c) <year> <copyright holders>