Exif metadata

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Exif, short for "Exchangeable image file format", is actually a standard for how image data, audio data and metadata tags should be formatted in jpeg and tiff images as well as wav audio files. "Exif" is most commonly used to describe metadata which is embedded into jpeg image files by cameras, phones and image manipulation software.

The standard

The actual exif specification covers metadata tags in compressed JPEG images files, uncompressed TIFF images, RIFF WAV audio and IMA-ADPCM compressed audio. The first version of the standard was written by the Japanese in the early 1990s. Version 2.1 was defined in June 1998 and an update to 2.2 was written in April 2002. The standard was again revised in 2010 and 2013. The latest version 2.3.2 was defined on May 17th, 2019.

Almost all cameras and mobile phone applications support the Exif metadata standard. Most digital photographs have exif metadata with at minimum

  • Camera/phone manufacturer
  • Camera/phone model
  • Orientation (rotation)
  • Date and time
  • Camera settings
  • An embedded thumbnail of the full image

There are a lot of other information which can be embedded into a digital photograph.

Software

exiftool is a handy program for viewing, editing or manipulating exif data embedded into images and a whole range of other file types and formats. It supports a wide range of operations. It's default behavior when ran with an image as an argument, exiftool imagefile.jpg, is to print out all the exif metadata in that image. It has a lot of options for manipulating exif data listed in it's manual page.

Exiftool-output.jpg
exiftool showing the exif data embedded in a typical image.

The command exiftool -all= imagefile.jpg will remove all exif data from an image while leaving a backup of the original file named imagefile.jpg_original behind.

Not-standard metadata

Some multi-national corporations embed special non-standard metadata into their images. Facebook embeds a "Special Instruction" with mysterious tracking information into all images uploaded to their platforms (Facebook/Instagram/etc).

This "Special Instruction" is not complaint with the Exif metadata standard. Software will not show it as part of the regular exif data. Some programs like geeqie can show all metadata embedded in images including non-exif data.

Facebook-special-instructions.jpg

Facebook-special-instructions-02.jpg

What is this special Facebook code for? Nobody knows. The mystery is unsolved.


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