(via shibuvarkala.blogspot.com)
ExifTool is a Perl module with an included command-line application
for reading and writing meta information in image, audio and video
files. Modern Digital Camera including Canon, Minolta,Konica, Nikon, Pentax store all the settings you used, such as aperture or shutter speed along with the picture. For extracting the camera settings and Picture information , you can use ExifTool. ExifTool is requred for profesional editing of some Picture Files.