I know this is an old issue and people have done work arounds, but building against libpng14 did create a lot of problems for linux users whose distros do not have libpng14 (something like 4 out of the top 5 distros, and 7 out of the top 10 don't have it). It appears now that they will never have libpng14. In fact, libpng's own website encourages the use of 12 or 15...
Could CadSoft either:
1) build against libpng15, if possible
2) include libpng.so.14 with the release or statically link against libpng14
CadSoft has said that (2) is impossible for legal reasons, but that doesn't make sense. libpng's license is:
" Permission is hereby granted to use, copy, modify, and distribute this
source code, or portions hereof, for any purpose, without fee, subject
to the following restrictions:
1. The origin of this source code must not be misrepresented.
2. Altered versions must be plainly marked as such and
must not be misrepresented as being the original source.
3. This Copyright notice may not be removed or altered from
any source or altered source distribution.
The Contributing Authors and Group 42, Inc. specifically permit, without
fee, and encourage the use of this source code as a component to
supporting the PNG file format in commercial products. If you use this
source code in a product, acknowledgment is not required but would be
appreciated."
Which allows, with no preconditions, CadSoft to include libpng14 with their binary for eagle. It explicitly says you can use it in commerical products and doesn't even require you to acknowledge that you did (although I would encourage you to). It's an extremely generous license which in fact allows you to even statically compile the library into eagle and distribute the binary that way (with the proper attribution in your readme or license file). However, that may be a security threat and thus a liabillity.
If you're worried about security, then you can do (1) and rely on distributions to keep the library up to date to reduce your liabillity.
Thanks for your consideration, and hopefully this is something that can be easily worked out.
