nanoexif is simple exif parser library. Written in plain C99(and uses some gcc extensions).
This module supports C99. I don't want to support legacy systems, but I can accept your patch.
libexif( http://libexif.sourceforge.net/ ) is most popular exif manupulation library.But it's under LGPL.
iphone-exif (http://code.google.com/p/iphone-exif/ ) is exif manipulation library for iPhone.It is only for iPhone, and wrapped under GPL.