The libpng license is a permissive free software license, which defines the terms under which the libpng

Libpng

libpng is the official Portable Network Graphics reference library . It is a platform-independent library that contains C functions for handling PNG images...

 software library can be distributed.

Origin and history

The libpng license was derived in 1996 from the zlib license

Zlib License

The zlib License is a permissive free software license which defines the terms under which the zlib and libpng software libraries can be distributed. It is also used by other free software packages....

 and has been referred to since by a variety of terms including at least the "zlib license" (even though it is different) and the "zlib/libpng license".
Standards/free software bodies such as OSI currently refer to the license as the "zlib/libpng license".
The license differs most significantly from the zlib license in including a clause for compatibility with the UCITA.
This was added around 2000 in response to the adoption of UCITA by the US state of Maryland

Maryland

Maryland is a U.S. state located in the Mid Atlantic region of the United States, bordering Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware to its east...

.

Since this was after the adoption of the license by OSI

Open Source Initiative

The Open Source Initiative is an organization dedicated to promoting open source software.The organization was founded in February 1998, by Bruce Perens and Eric S. Raymond, prompted by Netscape Communications Corporation publishing the source code for its flagship Netscape Communicator product...

 questions have been raised about the actual OSI status

External links

• The PNG file format home page http://www.libpng.org/pub/png/
• The libpng home page.
• The text of the license on the web page.