[Insight-developers] Linear algebra licensing and ITK 3.18 Release

[kent williams]

Correct me if I'm wrong but here's my executive overview of ITK licensing.

1. ITK itself is released with a BSD-like license, meaning that it's truly
Free software, in that anyone can use it any way they want to --
incorporating it into both open- and closed-source applications.

2. GPL has the 'viral hook' disadvantage, in that it forces anything
incorporating GPL-licensed software to also be GPL licensed.  This is
incompatible with ITK's license, so ITK doesn't incorporate GPL-licensed
software.

3. The Lesser GPL (LGPL) license is GPL minus the 'viral hook.' GLIBC is
released under GPL; otherwise no closed-source program would be legal on
Linux, or OSX.  LGPL libraries could potentially be incorporated into ITK.

4. Anything incorporated into ITK has to have an unambiguous software
license compatible with the ITK license.  Thus the current search to replace
the linear algebra stuff apparently under ACM license restrictions.

5. In extraordinary cases, (FFTW being the prime example), ITK will include
classes that depend on GPL-licensed libraries, but without including the
library as part of ITK. It's up to the ITK user to resolve their own
licensing questions if they configure ITK to use these GPL-licensed
libraries.