Portable Network Graphics (aka PNG) is an image file format developed to replace GIF images on the web. It uses lossless compression and is thus not ideal for photographs. The types of images ideally suited for PNG are line-art, text, other graphics that have sharp transitions.
A PNG file comprises "chunks" of data, some of which are mandatory and others of which are ancillary. Some ancillary chunks can contain metadata text or timestamps, but does not contain nearly as much metadata as exif images.
PNG files begin with the following 8-byte (hexadecimal) signature:
89 50 4E 47 0D 0A 1A 0A