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

ISO/IEC TS 20071-11:2012 applies to all static images that are used in any type of electronic document. It also applies to individual images within a slide show of electronic images. ISO/IEC TS 20071-11:2012 does not apply to moving images (e.g. movies). The guidance contained in ISO/IEC TS 20071-11:2012 is intended to be used by the person who creates content 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 ISO/IEC TS 20071-11:2012 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.

Technologies de l'information — Accessibilité du composant interface utilisateur — Partie 11: Lignes directrices pour le texte alternatif pour images

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Status
Withdrawn
Publication Date
12-Nov-2012
Withdrawal Date
12-Nov-2012
Current Stage
9599 - Withdrawal of International Standard
Start Date
16-Dec-2019
Completion Date
16-Dec-2019
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TECHNICAL ISO/IEC
SPECIFICATION TS
20071-11
First edition
2012-12-01
Information technology — User interface
component accessibility —
Part 11:
Guidance for alternative text for images
Technologies de l'information — Accessibilité du composant interface
utilisateur —
Partie 11: Lignes directrices pour le texte alternatif pour images
Reference number
ISO/IEC TS 20071-11:2012(E)
ISO/IEC 2012
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ISO/IEC TS 20071-11:2012(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO/IEC 2012

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,

electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or

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Published in Switzerland
ii © ISO/IEC 2012 – All rights reserved
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ISO/IEC TS 20071-11:2012(E)
Contents Page

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

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

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

2 Terms and definitions ........................................................................................................................... 1

2.1 Text alternatives and related definitions ............................................................................................. 1

2.2 Image and related definitions ............................................................................................................... 2

2.3 Importance and related definitions ...................................................................................................... 3

2.4 Information relationship definitions .................................................................................................... 3

2.5 Image content and related definitions ................................................................................................. 4

2.6 Image sources and related definitions ................................................................................................ 4

2.7 Information type definitions ................................................................................................................. 5

3 Framework for describing images and creating text alternatives .................................................... 6

3.1 Uses of text alternatives ....................................................................................................................... 6

3.2 Structure of descriptions ...................................................................................................................... 6

3.3 Structure of text alternatives ................................................................................................................ 7

4 Requirements and recommendations for describing images .......................................................... 8

4.1 A procedure for creating text alternatives .......................................................................................... 8

4.2 Purposes .............................................................................................................................................. 10

4.2.1 Introduction to purposes .................................................................................................................... 10

4.2.2 Informative purposes .......................................................................................................................... 10

4.2.3 Control purposes ................................................................................................................................. 11

4.2.4 Decorative purposes ........................................................................................................................... 11

4.2.5 Formatting purposes ........................................................................................................................... 12

4.2.6 Brevity of statements of purposes .................................................................................................... 12

4.3 Context of an image ............................................................................................................................ 13

4.3.1 Text alternatives relate an image to its context within a document .............................................. 13

4.3.2 Context of images within panels within a document ....................................................................... 13

4.4 Levels of importance ........................................................................................................................... 13

4.4.1 Importance is context dependent ...................................................................................................... 13

4.4.2 Importance ........................................................................................................................................... 14

4.5 Images and image components ......................................................................................................... 16

4.6 Identification of content ...................................................................................................................... 18

4.6.1 Introduction to identification of content ........................................................................................... 18

4.6.2 Subjective content ............................................................................................................................... 18

4.6.3 Objective content ................................................................................................................................ 18

4.6.4 Relationships of images and their components .............................................................................. 20

5 Expanding on the identification and elaboration of content .......................................................... 20

5.1 Introduction .......................................................................................................................................... 20

5.2 Detailed questions relating to identification ("what") ..................................................................... 21

5.2.1 Classifying the image (or image component) .................................................................................. 21

5.2.2 Elaborating on textual content ........................................................................................................... 22

5.2.3 Elaborating on physical objects ........................................................................................................ 22

5.2.4 Elaborating on people ......................................................................................................................... 22

5.2.5 Elaborating on perceptual objects and perceptual properties of other objects ........................... 22

5.2.6 Elaborating subjective descriptions .................................................................................................. 23

5.2.7 Elaborating on logical relationships / interactions and actions ..................................................... 23

5.2.8 Elaborating on locations/places ........................................................................................................ 24

5.3 Detailed questions relating to temporal elaboration ("when") ....................................................... 24

5.3.1 Introduction to temporal properties .................................................................................................. 24

5.3.2 Elaborating about time periods ......................................................................................................... 25

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ISO/IEC TS 20071-11:2012(E)

5.3.3 Elaborating about events / activities .................................................................................................25

5.3.4 Elaborating sequential relationships .................................................................................................25

5.3.5 Elaborating on states ..........................................................................................................................26

5.3.6 Elaborating on slide shows ................................................................................................................26

5.4 Detailed questions relating to physical (spatial) relationship elaboration ("where") ...................27

5.5 Detailed questions relating to quantitative elaboration ("how much") ..........................................27

5.6 Detailed questions relating to procedural elaboration ("how") ......................................................28

5.6.1 Elaborating on the intended use of the image ..................................................................................28

5.6.2 Elaborating on control ........................................................................................................................28

6 Guidance on writing text alternatives ................................................................................................28

6.1 Importance and purpose .....................................................................................................................28

6.2 Elaborating on the context of an image ............................................................................................28

6.3 Flow with the document content ........................................................................................................29

6.4 Story telling ..........................................................................................................................................29

6.5 Independence of importance from order ..........................................................................................29

7 Guidance on evaluating text alternatives ..........................................................................................29

Bibliography ......................................................................................................................................................30

iv © ISO/IEC 2012 – All rights reserved
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ISO/IEC TS 20071-11:2012(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. In the field of information

technology, ISO and IEC have established a joint technical committee, ISO/IEC JTC 1.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.

The main task of the joint technical committee is to prepare International Standards. Draft International

Standards adopted by the joint technical committee are circulated to national bodies for voting. Publication as

an International Standard requires approval by at least 75 % of the national bodies casting a vote.

In other circumstances, particularly when there is an urgent market requirement for such documents, the joint

technical committee may decide to publish an ISO/IEC Technical Specification (ISO/IEC TS), which

represents an agreement between the members of the joint technical committee and is accepted for

publication if it is approved by 2/3 of the members of the committee casting a vote.

An ISO/IEC TS is reviewed after three years in order to decide whether it will be confirmed for a further three

years, revised to become an International Standard, or withdrawn. If the ISO/IEC TS is confirmed, it is

reviewed again after a further three years, at which time it must either be transformed into an International

Standard or be withdrawn.

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

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

ISO/IEC TS 20071-11 was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology,

Subcommittee SC 35, User interfaces.
© ISO/IEC 2012 – All rights reserved v
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ISO/IEC TS 20071-11:2012(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 be used to present the user

with 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. This document provides guidance for web and document

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

vi © ISO/IEC 2012 – All rights reserved
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TECHNICAL SPECIFICATION ISO/IEC TS 20071-11:2012(E)
Information technology — User interface component
accessibility —
Part 11:
Guidance for alternative text for images
1 Scope

This part of ISO/IEC 20071 applies to all static images that are used in any type of electronic document. It also

applies to individual images within a slide show of electronic images.

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

the contents of this technical report are not dependent on the choice of implementation mechanism or of electronic

document type.
This part of ISO/IEC 20071 does not apply to moving images (e.g. movies).

The guidance contained in this part of ISO/IEC 20071 is intended to be used by the person who creates

content 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 part of ISO/IEC 20071 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.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1 Text alternatives and related definitions
2.1.1
text alternative
a textual description or representation of an image

NOTE 1 By storing this description or representation in text format, it is able to be rendered in any available modality.

NOTE 2 The main audience of text alternatives is the users of screen reading features.

NOTE 3 Text alternatives are often provided to screen reader users in the form of primary and secondary alternative

texts of an image.
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ISO/IEC TS 20071-11:2012(E)
2.1.2
primary alternative text
main text alternative provided to users of screen readers

NOTE Different technologies and platforms provide various mechanisms for containing and presenting primary

alternative text.

EXAMPLE In XHTML, HTML4, and HTML5, primary alternative text is provided in the “alt” attribute of the img tag.

EXAMPLE In Flash , primary alternative text is provided through the “Name” field.

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

2.1.3
secondary alternative text

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

NOTE Different technologies and platforms provide various mechanisms for containing and presenting secondary

alternative text.

EXAMPLE In XHTML and HTML4, secondary alternative text is provided in the “longdesc” attribute of the img tag.

EXAMPLE In Flash , secondary alternative text is provided through the “Description” field.

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

2.1.4
main document text
textual content of a document that is always presented to the users
2.2 Image and related definitions
2.2.1
image
graphical content intended to be presented visually

NOTE 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).
2.2.2
static image

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

NOTE 1 This includes images where the content/representation of individual image components might change over

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

NOTE 2 The concept of static image is used for all images that are not slide shows or moving images.

NOTE 3 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 might 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.”
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ISO/IEC TS 20071-11:2012(E)
2.2.3
slide show
set of images that replace one another periodically

NOTE 1 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 Slide shows are usually composed of static images, but might 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 staggered instead of smooth like in a movie.
2.2.4
moving image
image where the contents are dynamically changing

NOTE This includes realistic moving images (often referred to as movies), abstract moving images (often referred to

as cartoons), and even non-representational moving images (often referred to as light shows).

2.2.5
component

logical part of an image that provides important content that the user should be aware of

NOTE 1 Types of image component include (but not limited to) shapes, objects, persons, areas, and text.

NOTE 2 Text components can include natural and/or formal languages (such as mathematical equations).

2.3 Importance and related definitions
2.3.1
importance

level of need for users to know information about an image (or image

component)
2.3.2
essential

information that is necessary to understand the image and/or its function within

the document
2.3.3
significant

information that is needed for a more detailed understanding of the image

within the document to most users most of the time
2.3.4
helpful

information that provides a thorough understanding to target audiences

regarding the image within the document
2.3.5
not important

information that does not help provide additional understanding about the

image within the document to users
2.4 Information relationship definitions
2.4.1
relationship type
information about an association between entities
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ISO/IEC TS 20071-11:2012(E)
2.4.2
logical

information about what entities are interacting and how they interact

2.4.3
temporal
information about when some action or entity occurs
2.4.4
physical
spatial

information about where one entity is in relation to another entity

2.5 Image content and related definitions
2.5.1
content

data, information, objects, relationships, and/or concepts to be communicated from the originator to

the user according to certain communication goals
NOTE 1 Adapted from ISO 14915-1 definition 3.1.

NOTE 2 Content can be presented in realistic, abstract, or even non-representational manners. The distinction

between these types of presentation is how closely they represent the natural world.

2.5.2
realistic

image perceived by the user to faithfully represent data, information, objects, relationships,

and/or concepts in the natural world
NOTE Adapted from ISO 14915-3 definition 3.7.5.

EXAMPLE Photographic images, pictures intended to be true-to-life, diagrams used to illustrate how to assemble a

set of parts.
2.5.3
abstract

image intended to present important major data, information, object, relationship, and/or

conceptual components, without faithfully representing them as they occur in the natural world

EXAMPLE Cartoons, abstract art (where the basis for abstraction can be recognized), graphs and charts.

2.5.4
non-representational

image intended for decorative purposes without the intent to represent any particular natural

world data, information, objects, relationships, and/or concepts

EXAMPLE Art presenting colors and textures (without any recognizable objective contents).

2.6 Image sources and related definitions
2.6.1
source
means of obtaining an image (or image component)
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ISO/IEC TS 20071-11:2012(E)
2.6.2
photograph

electronic copy of an image of something that has its own independent existence in the real world

NOTE While the photograph is a true rendering of the object(s) that it illustrates, those objects can themselves be

realistic, abstract, or even non-representational.
2.6.3
electronic drawing
image created as an original work to be rendered on the computer

NOTE Electronic drawings can be realistic, abstract/non-representational and can contain realistic,

abstract/non-representational components. They can even contain embedded photographs as components.

2.7 Information type definitions
2.7.1
physical

information about phenomena which have a concrete existence; objects,

agents, or scenes that have a physical existence
[14915-3 definition 3.6.7]
NOTE This can include states and histories of objects.
2.7.2
value

quantitative information describing properties of an object

[14915-3 definition 3.6.12]
2.7.3
quantitative

statistical information or numerical data and the relationships between the

numbers
NOTE 1 Quantitative information is often presented in a graphical manner.

NOTE 2 Quantitative images are often used for comparison between related sets of data, such as comparing net profit

over a period of time.
NOTE 3 Examples of quantitative images include charts and graphs.
2.7.4
control

information that can be used to take some action which manipulates data, other

objects or their attributes
NOTE Adapted from ISO 14915-2 definition 3.8.
2.7.5
event

information about a state change, message indicating the occurrence of an

action, or conveying a significant change in the world
[14915-3 definition 3.6.6]
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ISO/IEC TS 20071-11:2012(E)
2.7.6
state

properties of the environment, objects or agents that remain constant during a

period of time
[14915-3 definition 3.6.11]
3 Framework for describing images and creating text alternatives
3.1 Uses of text alternatives

Images are often used to convey a large amount of information quickly, whether it is a diagram for

constructing a desk or a photo of what happened at a birthday party. In one glance, a person can retrieve a

large amount of information and have a general understanding about the remaining content in the document in

which the image resides.

Images are sometimes used to supplement or complement the document content or can be another

representation of the same content. However, sometimes the image stands alone or adds information that is

not part of the other document content. The information that is present in the image but not the other

document content does not get conveyed to those who are unable to see the image. Text alternatives are

needed to convey that information.

There are many reasons why a person might need text alternatives, including (but not limited to)

a) the person has a visual impairment;

b) the person is using a program that aurally reads the document content while doing something else (such

as driving or cooking);

c) the device being used to view the image is unable to properly display the image or the image is difficult to

see, (such as on a mobile device);

d) the person turned off images on their Web browser to increase loading speed; and

e) the person cannot understand and/or interpret the image.

Tools (such as screen readers) exist that can read aloud text that appears on a document to those who

cannot or are not looking at the screen. If an image can be described and represented textually, then the tools

can also read the text alternatives aloud.

Text alternatives might include a description of what the image looks like and/or an interpretation of what the

image represents or its function. Different text alternatives might exist for the same image, differing in length

and (as a result) information. Technology often allows for a primary alternative text as well as a secondary

alternative text. Providing both primary alternative text and secondary alternative text can give the user a

choice in the amount of detail they wish to receive about an image.
3.2 Structure of descriptions

In order to write informative text alternatives for an image, it is important to first know the information being

represented in the image. It is difficult to share knowledge about an image with others when the writer does

not have knowledge of what the image is. Therefore, it is important to gather or identify as much information

as possible about an image.
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ISO/IEC TS 20071-11:2012(E)

To gather as much information as possible, the following image description structure is used. Initially, the

structure identifies information about the whole image. It focuses on information that applies to the entire

image. Because an image can have a vast amount of information, the structure breaks down the image into

several parts (called image components) and focuses on identifying information about each part (or image

component). Breaking down the image into several parts allows for focus on the details of those particular

parts, resulting in more information about the image. An image component could be broken down further into

additional image components.

The structure of image information (illustrated in Figure 1) for the Whole Image and each image component

includes a name, the purpose, the basic image information or content, and the elaboration of the basic image

information. The name identifies the part of the image that the information applies. The purpose identifies why

the image (or image component) exists on the document. The basic image information or content identifies

what is in the image (or image component). The elaboration of the basic information looks at more specific

details about the image (or image component).
Figure 1 — Structure of image information

The intent of the structure is to identify as much information about an image as possible. The same piece of

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