Re: libpng license 2.0

On Thu, 6 Sep 2018, Cosmin Truta wrote:
>
> I'm prepending one more ("libpng license 2.0"), in the hope that this
> will be one last licensing update, and anything that follows shall be
> new one-liner copyright notices and copyright years only.

This seems like a reasonable plan, although the existing 
license/copyright text needs to also remain.

> There have been precedents with newer licenses superseding older ones.
> It's been rarely done, but it is possible, and the Mozilla Public
> License going from MPL-1.0 to MPL-1.1 to MPL-2.0 is a case in point.

Typically this can occur because the license allows updating to a 
later version, and/or the code is all signed away by contributors to 
one legal entity empowered to make such decisions.  I assume that 
Mozilla assures that the core code (e.g. for Firefox) is copyrighted 
by one entity.

> Relicensing without explicit approval of all copyright holders is not
> possible in general. It is possible only in a few exceptional cases.
> For example:
> * From GPLv2 to GPLv3 and from LGPLv2.1 to LGPLv3
> * From LGPLv2.1 to GPLv2 and from LGPLv3 to GPLv3
> * From 2-clause BSD to 3-clause BSD
> * From EUPL to GPL/LGPL/MPL/EPL/CPL/CeCILL

I have read that GPLv3 is not 100% compatible with GPLv2 and that it 
was expected that GPLv2 was applied as the license "How to Apply These 
Terms to Your New Programs" recommended such that later versions of 
the license could be used.

GNU programs developed by the FSF all require that contributors sign 
an agreement so that the code is copyrighted by the FSF.

As long as the new libpng license does not cause any conflict with 
existing text, it should be fine and all new contributions would be 
submitted under the new license.

Bob
-- 
Bob Friesenhahn
[email protected], http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/

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