Jhead is a command line program for manipulating the non-image
parts of Exif JPEG files that most digital cameras produce.  

By default, jhead displays the more useful camera settings from the
file, but it can also be used to perform operations such as changing
timestamps or removing a thumbnail.

Though there are many programs out there now that can manipulate
Exif headers today, for many tasks, jhead remains the simplest and
most effective tool for the job, especially if used for automated
or scripted tasks. 

Homepage: http://www.sentex.net/~mwandel/jhead/