EXIF

EXIF is EXchangeable Image File, about 2K header in jpeg file
0xFF+Marker Number(1 byte)+Data size(2 bytes)+Data(n bytes)
Example
File date : 2004:11:01 21:30:49
Camera make : NIKON
Camera model : E4500
Date/Time : 2004:10:31 15:11:21
Resolution : 1024 x 768
Flash used : No
Focal length : 14.4mm
Exposure time: 0.0034 s (1/298)
Aperture : f/4.7
ISO equiv. : 100
Metering Mode: matrix
Exposure : program (auto)

How to read EXIF?
UNIX-like OS: use jhead
Windows XP: right click image file, select property, in 2nd label, click advanced