From wikipedia
Exchangeable image file format (Exif) is a specification for the image file format used by digital cameras. It was written by the Japan Electronic Industry Development Association (JEIDA). The specification uses existing file formats such as JPEG, TIFF Rev. 6.0 and RIFF WAVE audio file format, with the addition of specific metadata tags. It's not supported in JPEG 2000 or PNG.
Version 2.1 of the specification is dated June 12, 1998 and version 2.2 is dated April 2002.
The metadata tags defined in the Exif standard cover a broad spectrum including:
* Date and time information. Digital cameras will record the current date and time and save this in the metadata.
* Camera settings. This includes static information such as the camera model and make, and information that varies with each image such as orientation, aperture, shutter speed, focal length, metering mode, and film speed information.
* Location information, which could come from a GPS receiver connected to the camera. As of 2004 only a few cameras support this, though. Some people therefore use a normal receiver to track their movements, and then post-process the images by matching the timestamps in the images with the log from the receiver and can so add the missing information to images.
* Descriptions and copyright information. Again this is something which is most often done when post-processing the images, as only high-end camera models let the user choose a text for these fields.
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