Portions of this computer program are copyright © 1995–2018 Celartem, Inc., doing business as Extensis.
All rights reserved.

MrSID libraries use the Intel Threaded Building Blocks (Intel TBB):
Intel TBB is used under the GNU General Public License, version 2, with the (libstdc++) runtime exception. Copyright © 2005 - 2013, Intel Corporation. https://www.threadingbuildingblocks.org/.

The runtime exception as documented on https://www.threadingbuildingblocks.org/Licensing allows unrestricted use of the MrSID library wrt. the GPLv2 license:
Runtime Exception
"As a special exception, you may use this file as part of a free software
library without restriction. Specifically, if other files instantiate
templates or use macros or inline functions from this file, or you compile
this file and link it with other files to produce an executable, this
file does not by itself cause the resulting executable to be covered by
the GNU General Public License. This exception does not however
invalidate any other reasons why the executable file might be covered by
the GNU General Public License."