From the libpng homepage...

 The libpng 1.5.x series continues the evolution of the libpng API,
 finally hiding the contents of the venerable and hoary png_struct and
 png_info data structures inside private (i.e., non-installed) header
 files. Instead of direct struct-access, applications should be using
 the various png_get_xxx() and png_set_xxx() accessor functions, which
 have existed for almost as long as libpng itself. (Apps that compiled
 against libpng 1.4 without warnings about deprecated features should
 happily compile against 1.5, too.

 Patch origin: Fedora packagers of libXcomp3.