ISO/IEC 20071-11:2019

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 2019
© ISO/IEC 2019
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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ii © ISO/IEC 2019 – All rights reserved

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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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

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

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

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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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 staggered instead of smooth like in a movie.
2 © ISO/IEC 2019 – All rights reserved

3.2.4
moving image
image where the contents are dynamically changing
Note 1 to entry: 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).
3.2.5
component
identifiable part of an image that provides content for the user
Note 1 to entry: Types of image component include (but not limited to) shapes, objects, persons, areas, and text.
Note 2 to entry: Text components can include natural and/or formal languages (such as mathematical equations).
3.3 Image types and related definitions
3.3.1
drawing
image created as an original work through the artistic actions of a human
3.3.2
photograph
electronic copy of an image of something that has its own independent existence in the real world
3.3.3
diagram
image containing a graphical representation of a set of (physical, logical, conceptual or other)
objects or components and their (physical, logical, sequential or other) relationships
3.3.4
map
image containing a geospatial representation of geographic data
3.3.5
computer-generated illustration
image created by a computer based on data that it has available to it
3.3.6
composite image
image created by combining individual images or components of individual images, which can
each be accessed as independent components of the composite image
3.4 Image content and related definitions
3.4.1
content
interactive or non-interactive object containing information represented by text, image, video, sound or
other media
[SOURCE: ISO/IEC/IEEE 23026:2015, 4.6]
3.4.2
realistic
content perceived by the user to faithfully represent data, information, objects,
relationships and/or concepts in the natural world
EXAMPLE Photographic images, pictures intended to be true-to-life, diagrams used to illustrate how to
assemble a set of parts.
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3.4.3
sketch
rapidly executed freehand drawing that is not usually intended as a finished fully-
realistic work
Note 1 to entry: Sketches are often monochrome line drawings, with or without shading.
3.4.4
caricature
content showing the features of its subject in a simplified or exaggerated way
3.4.5
cartoon
semi-realistic content that is usually intended to be entertaining
Note 1 to entry: It is typical for cartoons to include unrealistic situations, e.g. animals talking, people performing
physical actions that are not possible.
3.4.6
abstract
content 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.
3.4.7
non-representational
content 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).
Note 1 to entry: Diagrams, maps and computer-generated illustrations are often presented as composite images.
3.5 Information relationship definitions
3.5.1
relationship type
information about an association between entities
3.5.2
logical
information about what entities are interacting and how they interact
3.5.3
temporal
information about when some action or entity occurs
3.5.4
physical
spatial
information about where one entity is in relation to another entity
3.6 Information type definitions
3.6.1
physical
information about phenomena which have a concrete existence
EXAMPLE Objects, agents or scenes that have a physical existence.
Note 1 to entry: This can include states and histories of objects.
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3.6.2
value
quantitative information describing properties of an object
3.6.3
quantitative
statistical information or numerical data and the relationships between the numbers
Note 1 to entry: Quantitative information is often presented in a graphical manner.
Note 2 to entry: Quantitative images are often used for comparison between related sets of data, such as
comparing net profit over a period of time.
Note 3 to entry: Examples of quantitative images include charts and graphs.
3.6.4
control
information that can be used to take some action which manipulates data, other objects
or their attributes
3.6.5
event
information about a state change, message indicating the occurrence of an action, or
conveying a significant change in the world
3.6.6
state
properties of the environment, objects or agents that remain constant during a
period of time
3.7 Importance and related definitions
3.7.1
importance
level of need for users to know information about content
[SOURCE: ISO/IEC 20071-23, 3.11]
3.7.2
essential information
information that is necessary to understand the content and/or its function
[SOURCE: ISO/IEC 20071-23, 3.12]
3.7.3
significant information
information that is needed for a more detailed understanding of the content and/or its function to most
users most of the time
[SOURCE: ISO/IEC 20071-23, 3.13]
3.7.4
helpful information
information that provides a thorough understanding of the content to some users
[SOURCE: ISO/IEC 20071-23, 3.14]
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3.7.5
unhelpful information
information that does not help users understand the content and/or can interfere with that
understanding
[SOURCE: ISO/IEC 20071-23, 3.15]
4 Text alternatives for images
4.1 Uses of text alternatives
Images are often used to convey a large amount of information, 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.
NOTE 1 While text alternatives are primarily developed for electronic documents (including computer
applications, apps, and websites); they can also be helpful in printed documents that can be read out to a user.
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. Any 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 can 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
(e.g. the person is listening while 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 small mobile device);
d) the person turned off images on their web browser to increase loading speed;
e) the person cannot understand and/or interpret the image; and
f) the text alternative can be used by search engines to find an image.
Tools (such as screen readers) exist that can read aloud text that appears in 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.
NOTE 2 The term "text alternative" is used to represent the text equivalent of an image, regardless of where
that text resides. The term "alternative text" is generally used to represent a text alternative that is technically
provided as an attribute of an image.
Text alternatives can include a description of what the image looks like and/or an interpretation of what
the image represents or its function. Different text alternatives can be developed 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 to be attached as attributes of an image. 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.
Images can mean different things to different viewers. However, images are added to a document
for particular purposes with the intent of meaning certain things to all viewers. In order to write
informative text alternatives for an image, it is important to first know the information intended to be
represented in the image. It is difficult to share knowledge about an image with others if the alternative
6 © ISO/IEC 2019 – All rights reserved

text developer does not have knowledge of what the image is intended to convey to the reader. Therefore,
it is important to gather or identify as much information as possible about an image.
It is preferable for the developer of the electronic document to also be the developer of text alternatives
for images included in the document.
NOTE 3 While various experts can analyse an image to a greater extent (e.g. for cataloguing purposes in a
library of images), it important that people involved in this procedure understand the information content that
the image is intended to convey within the document in which it occurs.
This document presents a method for identifying information about an image and then structuring text
alternatives for the image.
4.2 Presenting text alternatives
4.2.1 General
There are three possible locations for presenting text alternatives for an image:
a) within the main body of text;
b) within the primary alternative text attribute of an image;
c) within the secondary alternative text attribute of an image or within secondary alternative text
that is linked in some manner to the image.
NOTE Subclause 10.4 provides guidance on the use of these three locations for presenting text alternatives.
4.2.2 Text alternatives within the main body of text
The information contained in well-written text alternatives can often help users who can see an image
to understand or interpret the image as it was intended by the document developer. In situations
where the information contained in a text alternative is considered beneficial to all (or most) users of a
document, this information can be presented in the main body of text, either as part of the main text or
in a special addition to the main text that is identified as acting as a text alternative to the image, rather
than as alternative text attribute of the image that requires special efforts to access.
Where text alternatives are included within the main body of text, they are not limited in length and
can take one or more paragraphs to provide detailed descriptions of the image and detailed discussions
of its intended purpose.
4.2.3 Primary alternative text
Primary alternative text is the usual location for text alternatives for images in most documents. The
primary alternative text is usually displayed (in a hidden manner) to tools such as screen readers. Some
tools present the primary alternative text automatically by default, while the user needs to request the
secondary alternative text.
Where alternative text is considered beneficial for all readers it can be placed (with a suitable notation
identifying it as alternative text) in the main body of text, as long as the primary alternative text is used
to refer to the location of it in the main body of text (see subclause 10.4.6).
Some types of electronic documents have a limitation or restriction on the length of the primary
alternative text.
NOTE Some screen readers will sub-divide alternative text entries that are larger than 125 characters.
In order to limit the size of the primary alternative text, it is often viewed as an overview of the image
content, what the image is about, or the function of the image.
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Short primary alternative texts (due to character length limitations) may not be sufficient to convey
the full amount of information provided by the image. Where primary alternative texts are limited
in length, secondary alternative text becomes an important means of communicating the complete
meaning/content of an image.
4.2.4 Secondary alternative text
Where it is available, secondary alternative text generally does not have limits on its length and
therefore can contain a larger amount of information about the image. It can consist of details about the
image that could not be part of the primary alternative text.
Since there is no limit on the amount of information, it can include information that some users might
not need. The importance of each piece of information about an image can help to determine if the
information is presented in the primary alternative text, secondary alternative text, both primary and
secondary alternative texts, or not at all (see Clause 10 for a discussion of levels of importance).
5 Procedure for creating text alternatives
The creation of suitable text alternatives (regardless of where they are located) shall be based on a
thorough understanding of the image, its components, its purpose and context in the document where
it is contained.
This can be done by applying the following procedure:
a) Identify the type of image (Clause 6)
Identify the type (and if applicable the sub-type) of image.
b) Identify the purpose of the image (Clause 7)
Identify and describe the purpose of each image. This step influences which image components and
which pieces of information are important for the user to know.
This involves answering the question "Why?"
c) Identify the image components (Clause 8)
Depending on the purpose of the image, identify the image components. This step is necessary to
properly identify pieces of information about the image that can be important to the user.
This can be done in a two-stage process:
1) Identify the image as a whole;
2) Identify the image components of the image.
NOTE 1 Identifying image components is an iterative proces
...