FindPNG
: Find the native PNG includes and libraryThis module defines
PNG_INCLUDE_DIR, where to find png.h, etc.
PNG_LIBRARIES, the libraries to link against to use PNG.
PNG_DEFINITIONS - You should add_definitons(${PNG_DEFINITIONS}) before compiling code that includes png library files.
PNG_FOUND, If false, do not try to use PNG.
also defined, but not for general use are
PNG_LIBRARY, where to find the PNG library.
None of the above will be defined unles zlib can be found. PNG depends on Zlib