Exchangeable Image File Format

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The Exchangeable Image File Format (official abbreviation Exif ) is a standard format of the Japan Electronic and Information Technology Industries Association ( JEITA ) for the storage of metadata in digital images. The last version of the standard (2.32, April 2010, last revision in May 2019) was formulated by a cooperation between JEITA and the Japanese organization CIPA ( Camera & Imaging Products Association , successor organization to JCIA - Japan Camera Industry Association).

Technical information on the recording, including camera model, time of recording and camera settings, is stored in the Exif data of an image file.

Other metadata standards are the IPTC-IIM standard and the Extensible Metadata Platform (XMP).

Areas of application

Exif data is written directly into the file of images in JFIF (JPEG) or TIFF formats - in the so-called header (area at the beginning of the image file, before the actual image information). In the meantime, practically every digital camera stores this additional information about the recording in the picture, and the camera applications of most smartphones also create pictures with Exif data.

Numerous image processing programs and other software can output this data. In addition, Exif data can be used for audio files.

Exif entries

Almost all modern digital cameras can use the Exif standard and save numerous recording parameters with each shot, such as:

Further useful information can be added later in the form of so-called IPTC data (International Press Telecommunications Council). In addition to Exif, the IPTC standard is another standard that is mainly used in photojournalism . Examples of typical IPTC fields are:

Examples of exif tags

Displaying the metadata (binary Exif data, IPTC-NAA data and XMP) of a JPEG photo in Mozilla SeaMonkey

There is various information in the Exif data, they are stored in the form of so-called "tags" (English "tag" = identification, marking). The tags each consist of a pair of a name and a value. The values ​​can be of different types and lengths. For clear identification, each tag has a number (tag ID) consisting of 16 bits, which can be represented as a decimal number or four hexadecimal digits (with the suffix “.H” according to the standard or often with the prefix “0x”). The national language representation of the names and the formatting of the (numerical) values ​​is done by display programs. The tags are standardized and provide information about the camera settings under which the picture was taken, such as the following:

Exif tags and their meaning
ID (hex.) Surname meaning
9000 ExifVersion Version of the Exif standard
010F Make Name of the camera manufacturer
0110 Model Name of the camera model
0112 Orientation Image orientation portrait / landscape
9003 DateTimeOriginal Recording date
829D FNumber F-number
829A ExposureTime Exposure time
8833 ISOSpeed Image sensor sensitivity
9207 MeteringMode Exposure metering method average / spot / multi-segment
013B artist Creator / photographer
8298 copyright Copyright information
9286 UserComment General comment or image description. Unicode capable
010e ImageDescription Title of the picture and brief description of the picture

In addition to the standard fields, manufacturers can also insert specific "maker notes" that contain manufacturer-defined, proprietary information that is either not defined by the Exif standard or whose content is not disclosed for other reasons. Examples:

  • Focus mode
  • AF point
  • Focus Distance
  • Total Pictures

Example of Exif data of a picture taken with a Sony Alpha 380

Name of the saved file DSC04923.ARW
Camera model Sony Alpha 380
Firmware Firmware version 1.1
Recording date / time November 27, 2011 3:39:28 PM
Author / photographer John Doe
Copyright notice Copyright: Max Mustermann
Name of the owner John Doe
Recording mode A (aperture priority)
Tv ( shutter speed ) 1/6
Av ( f-number ) 2.8
Measurement mode Multi-field measurement
Exposure compensation 0
Film speed (ISO) 100
Automatic film speed (ISO) Out
lens Sony AF 20mm F2.8
Focal length 20.0 mm
Image size 4600 × 3064
picture quality Fine
lightning Out
FE flash exposure lock Out
White balance Automatically
AF mode Manual focus
Color space sRGB
Color depth 36 bits
Noise Reduction for Long Exposure 0: Off
Automatic exposure optimization 0: standard
Edge light correction Activate
File size 18842 KB
Dust extinguishing data No
mode of transport Single shot
Live image recording Out

The data from the objective can be used by panorama programs to correct certain imaging errors before assembly. This camera and the associated software also use the data for peripheral light correction in order to eliminate slight vignetting caused by brightening.

Possible problems

privacy

With the metadata automatically saved by the camera, details such as date, time, location, preview image etc. may inadvertently be passed on or published. Depending on your point of view, this can be desirable or undesirable. So was z. For example, the whereabouts of the then volatile John McAfee is known through the careless publication of a photo with GPS coordinates taken during an interview with a journalist.

At least the company Google uses the EXIF ​​data, the file name and alternative image texts in order to better understand the images.

Matt Cutt, a former employee at Google, said in 2014 that EXIF ​​data from images could possibly be a ranking factor for Google Image:

"It's something that Google can analyze and I think we reserve the right to use it in the ranking!"

Conversely, there is a controversy as to whether search engine optimization (SEO) can be carried out using the image information.

With the help of suitable computer programs, all Exif data can be removed from image files.

The company Facebook Inc. automatically removes metadata from on Facebook uploaded images. The company was banned from doing this in Germany in 2016. The judgment was justified with the deleted evidence of the author. Image metadata may not be removed or changed without authorization in accordance with Section 95c of the Copyright Act . Image files from which it is known that metadata has been removed without authorization may not be redistributed without authorization.

compatibility

When editing photos with common image editing programs, some Exif data can be changed in such a way that they are no longer displayed with common image viewers. The problem arises from the fact that, according to the JFIF specification, the JFIF-APP0 marker must be located directly behind the SOI marker, while according to the Exif specification, the Exif-APP1 marker must be located there. Strictly speaking, inserting Exif data into a JFIF file creates a different file format that is not JFIF compliant. However, newer JFIF libraries (e.g. from the Independent JPEG Group (IJG) from 2001) recognize existing Exif data and then leave the Exif APP1 marker unchanged.

Time zones

Right from the start, the Exif specifications did not define any time zones. There is no standard time zone such as B. UTC specified. Therefore problems with the date and time can occur when exchanging images across different time zones or when switching between summer and winter time. It was not until Exif version 2.31 (July 2016) that time zone tags were introduced: “OffsetTime”, “OffsetTimeOriginal” and “OffsetTimeDigitized”.

Embedding malicious code

Using the Exif metadata area, it is possible to smuggle in and execute program code on external web servers. To do this, an image is uploaded to the server using a file upload form. However, this has the extension of an executable file (for example .aspx or .php). However, based on the actual content, the server assumes a harmless picture. The actual malicious code is located as metadata in the Exif area. If the manipulated file is then retrieved from the server via a URL , it is executed based on the file extension instead of being displayed. In the next step, the database or the domain controller can be taken over. If the server checks when the file is uploaded whether the file extension matches the actual content, such an attack is impossible.

Versions

  • 2.1 of 0June 1, 1998
  • 2.2 0(project name "Exif Print") of February 20, 2002 (published between February and April 2002)
  • 2.21 (with Adobe RGB support) from July 11, 2003 (published in September 2003 immediately after DCF 2.0)
  • 2.3 0of April 26, 2010, revision May 2013
  • 2.31 of April 26, 2010, revision April 2016

Web links

Commons : Exif  - collection of images, videos and audio files

Software and tools

Individual evidence

  1. ↑ CIPA / JEITA : Exif specification 2.32. (PDF) In: CIPA website. Retrieved May 1, 2019, December 17, 2019 (English translation of the relevant original Japanese document).
  2. ↑ sno.phy.queensu.ca: EXIF ​​tags
  3. ↑ Achim Sawall: John McAfee located with iPhone geolocation. Golem.de, December 4, 2012, accessed October 5, 2013 .
  4. ↑ a b https://imageseo.io/does-exif-iptc-impact-images-seo/ Does EXIF ​​data impact image SEO?, Online article by ImageSEO, accessed on May 7, 2020
  5. ↑ Hamburg Regional Court, file number 308 O 48/15
  6. ↑ https://www.ds-law.eu/lg-hamburg-iptc-daten-facebook/ LG Hamburg confirms protection of IPTC data on Facebook , message on D. Seiler's private website of November 20, 2016, accessed on May 7, 2020
  7. ↑ https://dejure.org/gesetze/UrhG/95c.html Copyright Act Part 4, Section 95c: Protection of the information required for rights management , Section 3
  8. ↑ Guido full conditions: Exif Patch Document. January 7, 2001, accessed June 10, 2015 .
  9. ↑ CIPA / JEITA : Exif specification 2.31. (PDF) In: CIPA website. July 14, 2016, Retrieved May 25, 2017 (English translation of the relevant original Japanese document).