Libkexif is a library for manipulating EXIF information embedded in images.
It currently supports viewing of all EXIF information via libexif. It also
supports the modification of a few attributes in a safe way that preserves
all other EXIF information in the file. It can currently modify the following
tags:

IFD0/Orientation
EXIF/UserCommend

WWW: http://digikam.sourceforge.net/