Found a nice & small utility from Matthias Wandel that manipulate EXIF data inside JPEG files.

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

Jhead v2.6 program Features

• Extracting camera settings from Exif image files
• Able to set and/or adjust the Exif time field
• Manipulation (extrac, replace, regenerate) of Exif integral thumbnails
• Transplant Exif image header from one JPEG to another
  Edit JPEG comment fields
• Automatically rotate images upright (using jpegtran) according to "orientation" tag.
• Manage running programs on large batches of Jpegs and restoring Exif header information afterwards.
• Display embedded GPS info (if present)