<s>
libpng	B-Language
is	O
the	O
official	O
Portable	O
Network	O
Graphics	O
(	O
PNG	O
)	O
reference	O
library	B-Library
(	O
originally	O
called	O
pnglib	B-Language
)	O
.	O
</s>
<s>
It	O
is	O
a	O
platform-independent	B-Operating_System
library	B-Library
that	O
contains	O
C	B-Language
functions	O
for	O
handling	O
PNG	O
images	O
.	O
</s>
<s>
libpng	B-Language
is	O
dependent	O
on	O
zlib	B-Language
for	O
data	O
compression	O
and	O
decompression	O
routines	O
.	O
</s>
<s>
libpng	B-Language
is	O
released	O
under	O
the	O
libpng	B-License
license	I-License
,	O
a	O
permissive	B-License
free	I-License
software	I-License
licence	I-License
,	O
and	O
is	O
free	B-Application
software	I-Application
.	O
</s>
<s>
It	O
is	O
frequently	O
used	O
in	O
both	O
free	B-Application
and	O
proprietary	B-Application
software	I-Application
,	O
either	O
directly	O
or	O
through	O
the	O
use	O
of	O
a	O
higher	O
level	O
image	B-Library
library	I-Library
.	O
</s>
