Information technology — User interface component accessibility — Part 11: Guidance on text alternatives for images

This document gives guidance on how to create text alternatives and what information to put in text alternatives. This document applies to all static images that are used in any type of electronic document. It also applies to individual images within a slide show. This document does not apply to moving images (e.g. movies). NOTE 1 While text alternatives can be implemented via various mechanisms in various types of electronic documents, the contents of this document are not dependent on the choice of implementation mechanism or of electronic document type. NOTE 2 Guidance on making moving images accessible is contained in ISO/IEC TS 20071-21, ISO/IEC 20071-23 and ISO/IEC 20071-25.

Technologies de l'information — Accessibilité du composant interface utilisateur — Partie 11: Lignes directrices pour les textes alternatifs pour images

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Status
Published
Publication Date
15-Dec-2019
Current Stage
6060 - International Standard published
Start Date
16-Dec-2019
Completion Date
16-Dec-2019
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INTERNATIONAL ISO/IEC
STANDARD 20071-11
First edition
2019-12
Information technology — User
interface component accessibility —
Part 11:
Guidance on text alternatives for
images
Technologies de l'information — Accessibilité du composant interface
utilisateur —
Partie 11: Lignes directrices pour les textes alternatifs pour images
Reference number
ISO/IEC 20071-11:2019(E)
ISO/IEC 2019
---------------------- Page: 1 ----------------------
ISO/IEC 20071-11:2019(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO/IEC 2019

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

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Published in Switzerland
ii © ISO/IEC 2019 – All rights reserved
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ISO/IEC 20071-11:2019(E)
Contents Page

Foreword ..........................................................................................................................................................................................................................................v

Introduction ................................................................................................................................................................................................................................vi

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

3.1 Text alternatives and related definitions .......................................................................................................................... 1

3.2 Image and related definitions .................................................................................................................................................... 2

3.3 Image types and related definitions ..................................................................................................................................... 3

3.4 Image content and related definitions................................................................................................................................ 3

3.5 Information relationship definitions ................................................................................................................................... 4

3.6 Information type definitions ....................................................................................................................................................... 4

3.7 Importance and related definitions ...................................................................................................................................... 5

4 Text alternatives for images ..................................................................................................................................................................... 6

4.1 Uses of text alternatives .................................................................................................................................................................. 6

4.2 Presenting text alternatives ......................................................................................................................................................... 7

4.2.1 General...................................................................................................................................................................................... 7

4.2.2 Text alternatives within the main body of text ...................................................................................... 7

4.2.3 Primary alternative text ........................................................................................................................................... .. 7

4.2.4 Secondary alternative text ....................................................................................................................................... 8

5 Procedure for creating text alternatives ...................................................................................................................................... 8

6 Identifying the types of image ................................................................................................................................................................ 9

6.1 General ........................................................................................................................................................................................................... 9

6.2 Drawings ...................................................................................................................................................................................................... 9

6.3 Photographs ...........................................................................................................................................................................................10

6.4 Diagrams ...................................................................................................................................................................................................10

6.5 Maps ..............................................................................................................................................................................................................10

6.6 Computer-generated illustrations .......................................................................................................................................11

6.7 Composite images .............................................................................................................................................................................11

6.8 Identifying image type in text alternatives ..................................................................................................................11

6.8.1 Identifying the image type of single images ..........................................................................................11

6.8.2 Identifying image type of composite images with separately addressable

components .......................................................................................................................................................................11

7 Identifying the purpose of the image ...........................................................................................................................................12

7.1 Introduction to purposes ............................................................................................................................................................12

7.2 Informative purposes .....................................................................................................................................................................12

7.3 Control purposes ................................................................................................................................................................................13

7.4 Decorative purposes........................................................................................................................................................................13

7.4.1 Decorative images that convey affective information ...................................................................13

7.4.2 Decorative images with minimal information value ......................................................................13

7.5 Formatting purposes ......................................................................................................................................................................14

7.6 Identifying purpose in text alternatives .........................................................................................................................14

7.6.1 Describing the purpose ...........................................................................................................................................14

7.6.2 Stating the purpose briefly ...................................................................................................................................14

7.6.3 Avoiding redundancy with captions ............................................................................................................15

7.6.4 Considering the context of use..........................................................................................................................15

7.6.5 Considering both objective and subjective purposes ....................................................................15

7.6.6 Text alternatives for images used for formatting purposes .....................................................15

7.6.7 Further information for images used for informative purposes .........................................15

7.6.8 Further information for images used for control purposes ....................................................16

8 Identifying the image components .................................................................................................................................................16

8.1 Images and image components .............................................................................................................................................16

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ISO/IEC 20071-11:2019(E)

8.2 Text components ................................................................................................................................................................................16

8.3 Uniquely identifying image components .......................................................................................................................16

8.4 Structuring information about images and their components ...................................................................17

8.5 Dealing with image complexity .............................................................................................................................................18

8.5.1 Use of image components .....................................................................................................................................18

8.5.2 Textual information in images ..........................................................................................................................18

8.5.3 Information about whole images ...................................................................................................................19

8.5.4 Information about image components ......................................................................................................19

9 Identifying the information (content) presented by the image .......................................................................19

9.1 Content of an image or its components ..........................................................................................................................19

9.2 Subjective content .............................................................................................................................................................................19

9.3 Objective content ...............................................................................................................................................................................20

9.4 Relationship content .......................................................................................................................................................................21

9.4.1 Relationships ....................................................................................................................................................................21

9.4.2 Actions ...................................................................................................................................................................................21

9.4.3 Logical relationships .................................................................................................................................................22

9.4.4 Temporal relationships ...........................................................................................................................................22

9.4.5 Physical (spatial) relationships ........................................................................................................................23

9.5 Interaction content ...........................................................................................................................................................................24

9.6 Analysing the information presented by an image ...............................................................................................24

10 Evaluating the importance of the information about the image .....................................................................25

10.1 Importance is context dependent ........................................................................................................................................25

10.2 Importance ..............................................................................................................................................................................................25

10.2.1 Levels of importance .................................................................................................................................................25

10.2.2 Essential information................................................................................................................................................25

10.2.3 Significant information ........................................................................................................................................... .26

10.2.4 Helpful information ....................................................................................................................................................26

10.2.5 Not important information ..................................................................................................................................27

10.3 Textual content in images ...........................................................................................................................................................27

10.4 Using importance to allocate information to text alternatives ...................................................................28

10.4.1 Including subjective information in text alternatives ...................................................................28

10.4.2 Including objective information in text alternatives ......................................................................28

10.4.3 Including relationship information in text alternatives ..............................................................28

10.4.4 Including information on associated activities in text alternatives ..................................28

10.4.5 Dealing with large amounts of essential information ...................................................................28

10.4.6 Placing text alternatives in the main body of text ............................................................................28

10.4.7 Handling conflicting information ...................................................................................................................29

11 Compose the text alternatives .............................................................................................................................................................29

11.1 Composition ...........................................................................................................................................................................................29

11.2 Organizing the information .......................................................................................................................................................29

11.2.1 Eliminating duplications ........................................................................................................................................29

11.2.2 Fitting into the context of use of the image ...........................................................................................30

11.2.3 Independence of importance from order ................................................................................................30

11.3 Wording text alternatives ...........................................................................................................................................................30

11.3.1 Flow with the document content ....................................................................................................................30

11.3.2 Style ..........................................................................................................................................................................................30

11.3.3 Conciseness and readability ...............................................................................................................................31

11.4 Creating text alternatives ............................................................................................................................................................31

12 Evaluate the text alternative ..................................................................................................................................................................31

12.1 The range of evaluation issues ...............................................................................................................................................31

12.2 The range of evaluation methods and testers ...........................................................................................................31

Annex A (informative) Further elaboration of objective content of images .............................................................33

Annex B (informative) Further considerations for particular types of images ....................................................37

Bibliography .............................................................................................................................................................................................................................41

iv © ISO/IEC 2019 – All rights reserved
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ISO/IEC 20071-11:2019(E)
Foreword

ISO (the International Organization for Standardization) and IEC (the International Electrotechnical

Commission) form the specialized system for worldwide standardization. National bodies that

are members of ISO or IEC participate in the development of International Standards through

technical committees established by the respective organization to deal with particular fields of

technical activity. ISO and IEC technical committees collaborate in fields of mutual interest. Other

international organizations, governmental and non-governmental, in liaison with ISO and IEC, also

take part in the work.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for

the different types of document should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject

of patent rights. ISO and IEC shall not be held responsible for identifying any or all such patent

rights. Details of any patent rights identified during the development of the document will be in the

Introduction and/or on the ISO list of patent declarations received (see www .iso .org/ patents) or the IEC

list of patent declarations received (see http:// patents .iec .ch).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www .iso .org/

iso/ foreword .html.

This document was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology,

Subcommittee SC 35, User interfaces.

This first edition of ISO/IEC 20071-11 as an International Standard cancels and replaces the Technical

Specification (ISO/IEC TS 20071-11:2012), which has been technically revised.
The main changes compared to the Technical Specification are as follows:
— a major restructuring and simplification of the requirements;
— the addition of image type specific information in annexes.
A list of all parts in the ISO/IEC 20071 series can be found on the ISO website.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www .iso .org/ members .html.
© ISO/IEC 2019 – All rights reserved v
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ISO/IEC 20071-11:2019(E)
Introduction

The saying that "A picture is worth a thousand words" recognizes that images can present a wealth

of information. It is important that alternative textual descriptions or representations present a

comprehensive account of the purpose and content of images to people unable to see or interpret them.

Text alternatives help people who cannot see the images to understand what the image is of or the

purpose it serves by providing the same information in textual form. Text alternatives can be useful

to those with visual impairments, those who turned images off in order to improve webpage loading

speeds, and those who cannot understand the image being displayed. They can also aid search engines

in finding images. This document provides guidance for user interface, web and document developers

to help them create informative descriptions for various types of illustrations.

While some sources of guidance advocate that text alternatives be kept short, it is important that they

provide an equitable alternative to the image. ISO/IEC Guide 71 states "A system provides equitable

use if it allows diverse users to accomplish tasks in an identical manner whenever possible or in an

equivalent manner when an identical manner is not possible". This document provides guidance

intended to help developers create equitable text alternatives.

The guidance contained in this document is intended to be used by the person who creates content and/

or text alternatives to be placed in an electronic document. There is no expectation that this person will

have any additional expertise beyond understanding the contents of the document and why an image

was chosen to be placed within the document.

While the main intent of the guidance within this document is the creation of text alternatives, the

information identified in this guidance could be placed in the main document text, reducing the length

of the resulting text alternatives. However, placing information in the main document text does not

fully replace the function of having some text alternatives for each image.
vi © ISO/IEC 2019 – All rights reserved
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INTERNATIONAL STANDARD ISO/IEC 20071-11:2019(E)
Information technology — User interface component
accessibility —
Part 11:
Guidance on text alternatives for images
1 Scope

This document gives guidance on how to create text alternatives and what information to put in text

alternatives.

This document applies to all static images that are used in any type of electronic document. It also

applies to individual images within a slide show.
This document does not apply to moving images (e.g. movies).

NOTE 1 While text alternatives can be implemented via various mechanisms in various types of electronic

documents, the contents of this document are not dependent on the choice of implementation mechanism or of

electronic document type.

NOTE 2 Guidance on making moving images accessible is contained in ISO/IEC TS 20071-21, ISO/IEC 20071-23

and ISO/IEC 20071-25.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1 Text alternatives and related definitions
3.1.1
text alternative
alternative text
textual description or representation of an image

Note 1 to entry: By storing this description or representation in text format, it is able to be rendered in any

available modality.

Note 2 to entry: The main audience of text alternatives are the users of screen reading features.

Note 3 to entry: Text alternatives are often provided to screen reader users in the form of primary and secondary

alternative texts of an image.

Note 4 to entry: Generally, "text alternative" is used to refer to any text alternative, while "alternative text" is

used to refer to text alternatives for images that are contained in attributes of an image.

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ISO/IEC 20071-11:2019(E)
3.1.2
primary alternative text
main text alternative provided to users of screen readers

Note 1 to entry: Different technologies and platforms provide various mechanisms for containing and presenting

primary alternative text.

EXAMPLE 1 In HTML 5.2 and EPUB, primary alternative text is provided in the “alt” attribute of the img tag.

EXAMPLE 2 In PDF, primary alternative text is provided through the /Alt entry in a structure element’s

dictionary.
3.1.3
secondary alternative text

additional text alternative provided to users of screen readers beyond primary alternative text

Note 1 to entry: Different technologies and platforms provide various mechanisms for containing and presenting

secondary alternative text.

EXAMPLE 1 In HTML5.2, secondary alternative text is provided in the “longdesc” attribute of the img tag.

EXAMPLE 2 In EPUB, secondary alternative text is provided through the “role” attribute.

3.1.4
main body of text
textual content of a document that is always presented to the users
3.2 Image and related definitions
3.2.1
image
graphical content intended to be presented visually

Note 1 to entry: This includes graphics that are encoded in any electronic format, including, but not limited

to, formats that are comprised of individual pixels (e.g. those produced by paint programs or by photographic

means) and formats that comprised of formulas (e.g. those produced as scalable vector drawings).

3.2.2
static image

image where the set of image components and their relationships to one another do not change over time

Note 1 to entry: This includes images where the content/representation of individual image components can

change over time, e.g. indicators where the value they are indicating changes in real time.

Note 2 to entry: The concept of static image is used for all images that are not slide shows or moving images.

Note 3 to entry: This use of static image is similar to the ISO/IEC 13249-5 use of "still image". However, it differs

in that a static image can have moving components. ISO/IEC 13249-5 states "A still image user-defined type is

generic to image handling. It addresses the need to store, manage, and retrieve information based on aspects of

inherent image characteristics such as height, width, and format and based on image features such as average

color, color histogram, positional color, and texture. It also addresses the need to employ manipulation such as

rotation, scaling as well as similarity assessment".
3.2.3
slide show
set of images that replace one another periodically

Note 1 to entry: The replacement of one static image by another static image can be controlled automatically by

the system (in which case the timing for each image is usually predetermined) or manually by the user (where

the timing for each image is determined on a case by case basis).

Note 2 to entry: Slide shows are usually composed of static images but can include short movies. The interval

between static images in a slide show are considered longer than in a movie, such that the motion being portrayed

by the slide show would appear stagger
...

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