Exif is just the technical data, like exposition, focal and lens lenght.
i.e. in this pic
the exif data (viewed pressing " E " in irfanview), is this:
Make - Canon
Model - Canon EOS 50D
Orientation - Left bottom
XResolution - 72
YResolution - 72
ResolutionUnit - Inch
DateTime - 2009:04:05 00:15:20
Artist -
YCbCrPositioning - Co-Sited
Copyright -
ExifOffset - 360
ExposureTime - 1/320 seconds
FNumber - 5
ExposureProgram - Not defined
ISOSpeedRatings - 3200
ExifVersion - 0221
DateTimeOriginal - 2009:04:05 00:15:20
DateTimeDigitized - 2009:04:05 00:15:20
ComponentsConfiguration - YCbCr
ShutterSpeedValue - 1/332 seconds
ApertureValue - F 4.97
ExposureBiasValue - 0
MeteringMode - Multi-segment
Flash - Flash not fired, compulsory flash mode
FocalLength - 60 mm
UserComment -
SubsecTime - 62
SubsecTimeOriginal - 62
SubsecTimeDigitized - 62
FlashPixVersion - 0100
ColorSpace - sRGB
ExifImageWidth - 2352
ExifImageHeight - 1568
InteroperabilityOffset - 8602
FocalPlaneXResolution - 2630.87
FocalPlaneYResolution - 2626.47
FocalPlaneResolutionUnit - Inch
CustomRendered - Normal process
ExposureMode - Auto
White Balance - Auto
SceneCaptureType - Standard
GPS information: -
GPSVersionID - 2.2.0.0
Maker Note (Vendor): -
Macro mode - Normal
Self timer - Off
Quality - Fine
Flash mode - Not fired
Sequence mode - Single or Timer
Focus mode - One-Shot
Image size - Small
Easy shooting mode - Manual
Digital zoom - None
Contrast - Normal
Saturation - Normal
Sharpness - Low , -32769
ISO Value - 32767
Metering mode - Evaluative
Focus type - Auto
AF point selected -
Exposure mode - A-DEP
Focal length - 18 - 200 mm (1 mm)
Flash activity - Not fired
Flash details -
Focus mode 2 - 65535
White Balance - Auto
Sequence number - 0
Flash bias - 0 EV
Subject Distance - 0
Image Type - Canon EOS 50D
Firmware Version - Firmware Version 1.0.3
Owner Name -
Sharpness (0D) - 52236
File number - 000 - 0000
Sharpness (A0) - 3
Thumbnail: -
Compression - 6 (JPG)
XResolution - 72
YResolution - 72
ResolutionUnit - Inch
JpegIFOffset - 10536
JpegIFByteCount - 16613