pngcheck verifies the integrity of PNG, JNG and MNG files
(by checking the internal 32-bit CRCs [checksums] and decompressing
the image data); it can optionally dump almost all of the chunk-level
information in the image in human-readable form.
For example, it can be used to print the basic statistics about an image
(dimensions, bit depth, etc.); to list the color and transparency info
in its palette (assuming it has one); or to extract the embedded text
annotations. This is a command-line program with batch capabilities.

pngsplit - break a PNG, MNG or JNG image into constituent chunks
(numbered for easy reassembly)

png-fix-IDAT-windowsize - fix minor zlib-header breakage caused by
older libpng

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