Almost all digital cameras save JPEG files with EXIF (Exchangeable Image File) data. Camera settings and scene information are recorded by the camera into the image file. Examples of stored information are shutter speed, date and time a photo was taken, focal length, exposure compensation, metering pattern and if a flash was used.
(EXchangeable Image Format) Descriptive data (meta-data) in an image file that include the date the photo was taken, resolution, shutter speed, focal length and other camera settings. Developed in 1995 by JEIDA for JPEG images, EXIF data was later added to TIFF, RAW and other formats. Most digital cameras support EXIF and save the data in the file headers. However, when an image is edited, the EXIF data may sometimes be removed by the software.
EXIF Dates May Not Be the File Date
When photos are downloaded from the camera into the computer, the date assigned to the image files may be the date the photos were taken (EXIF date) or the date the photos were downloaded. Photo viewers may sort photos by the internal EXIF date without regard to file dates or name order. For example, Apple’s iDevices sort photos by EXIF date. In order to be displayed in a different sequence, they must be rearranged in Apple’s iPhoto application on the Mac and then downloaded. Source@: http://www.pcmag.com/encyclopedia_term/0,1237,t=EXIF&i=42848,00.asp
Privacy and security
Since the Exif tag contains information about the photo, it can pose a privacy issue. For example, a photo taken with a GPS-enabled camera can reveal the exact location and time it was taken, and the unique ID number of the device – this is all done by default – often without the user’s knowledge. By removing the Exif tag with software such as ExifTool before publishing, the photographer can avoid possible problems. Many users may be unaware that their photos are tagged in this manner. A whistleblower, journalist or political dissident relying on the protection of anonymity to allow them to report malfeasance by a criminal, corporate or government entity may find their safety compromised by this default data collection.
In December 2012, anti-virus programmer John McAfee was arrested in Guatamala while fleeing from alleged persecution in Belize, which shares a border. Vice (magazine) had published an exclusive interview with McAfee “on the run” that included a photo of McAfee with a Vice reporter taken with an Iphone 4S smart phone. The photo’s metadata included GPS coordinates locating McAfee in Guatamala, and he was captured two days later.