pngcheck is the official PNG tester and debugger. Originally
designed simply to test the CRCs within a PNG image file (e.g.,
to check for ASCII rather than binary transfer), it has since
been extended to check and optionally print almost all the
information about a PNG image and to verify that it conforms to
the PNG specification. It also includes partial support for MNG animations.  

WWW: http://www.libpng.org/pub/png/apps/pngcheck.html