[Draft] Module 3: Images and Graphics
Introduction
Courses based on this module:
- specify correct use of markup languages and CSS techniques to make images and graphics accessible
- describe some types of images from an accessibility perspective
- explain how alternative texts allow people with disabilities to access information contained in images and graphics
Learning Outcomes for Module
Students should be able to:
- explain how text alternatives allow people with disabilities to access information contained in images and graphics
- mark up and write alternative texts for images
- use CSS properties to style text decorations instead of images of text
- use markup languages to convey mathematical expressions instead of images of text
- code mechanisms to provide additional descriptions for images and graphics
Competencies
Skills required for this module.
Students:
- Completion of courses that include:
- Basic knowledge of:
- HTML
img
element - [HTML
picture
element]https://html.spec.whatwg.org/multipage/embedded-content.html#the-picture-element) - CSS Specifications
- HTML
Instructors:
- Applied expertise in teaching:
- WCAG 2 Success Criterion 1.1.1 Non-text Content
- WCAG 2 Success Criterion 1.4.5 Images of Text
- WCAG 2 Success Criterion 1.4.9 Images of Text (No Exception)
- WCAG 2 Success Criterion 4.1.2 Name, Role, Value
- HTML
img
element - Html
alt
attribute - HTML
longdesc
attribute - [HTML
picture
element]https://html.spec.whatwg.org/multipage/embedded-content.html#the-picture-element) - CSS Specifications
- ARIA
img
role - WAI-ARIA attributes
aria-label
,aria-labeledby
, andaria-describedby
Figure
andfigcaption
elements
- In-depth knowledge of:
Topics to Teach
Optional topics to achieve the learning outcomes.
Topic: Simple Images
Explain the purpose and scope of simple images and graphics, for example, functional, informative, and decorative. Mention scenarios where alternative texts allow people access information which would not be available otherwise. Relate these strategies to WCAG success criterion 1.1.1 Non-text Content.
Learning Outcomes for Topic
Students should be able to:
- code HTML elements
picture
,img
, and<input type="image">
, as well as SVG graphics, using the HTML attributesalt
,title
,aria-label
, oraria-labelledby
- define the purpose and scope of simple images, such as functional, informative, and decorative images
- explain how text alternatives are read aloud by text-to-speech technologies
- explain how alternative texts can be visualized from mobile devices when images are turned off due to data restrictions
- explain how text alternatives are used for better image indexing and ranking
Teaching Ideas for Topic
Optional ideas to teach the learning outcomes:
- Explain that the HTML attribute
alt
should contain concise and clear information about the image. State that it is not necessary to include the word “image” in the alternative text since that would be separately announced via the HTML elementimg
. Mention that when an image is decorative, the value for thealt
attribute should be empty (“”), and, whenever possible, the image should be included in the web page using CSS instead of the HTML elementimg
. For reference on how to usealt
to code alternative texts, see techniques H2: Combining adjacent image and text links for the same resource and H37: Using alt attributes onimg
elements. - Demonstrate use of other ways to convey alternative texts, such as the HTML attributes
title
,aria-label
, oraria-labelledby
. Explain that these may not be well supported by old browsers and assistive technologies. For reference on how to usearia-label
andaria-labelledby
to provide descriptions for images, see techniques ARIA6: Using aria-label to provide labels for objects and ARIA10: Using aria-labelledby to provide a text alternative for non-text content. - Show examples of functional, informative, and decorative images and define their scope and purpose. Show the same image in different web pages and explain that an image can belong to different types depending on the context. For references on functional, informative, and decorative images, see the WAI website tutorials, Decorative Images, Informative Images, and Functional Images.
- Demonstrate use of commands, keystrokes, or gestures of text-to-speech technologies to move to next or previous image. Explore advanced functionality which presents all images in a list where users can select the image they are interested in. For reference on how people with disabilities interact and navigate web pages, see Stories of Web Users.
- Explain that images may not be available because of data restrictions or slow connections. Turn off images using common extensions or the settings screen in most browsers. Show and compare pages with and without alternative texts. Emphasize how essential information is often missed due to the lack of alternative texts.
- Explain that alternative texts are one of the techniques used by search engines to determine what an image is about. Indicate that the more accurate an alternative text is, the better your images could rank.
Ideas to Assess Knowledge for Topic
Optional ideas to support assessment.
- Short Answer Questions — Students are asked about the different HTML and WAI-ARIA elements and attributes to provide alternative texts for images. Assess students’ knowledge of the different coding techniques to provide alternative texts for images.
- Practical — Students provide alternative texts for a given set of functional, informative, and decorative images. Assess how students relate a given image with its specific function within a website.
- Practical — Students are presented with the same image in different contexts and are asked to provide the corresponding alternative text for each. Assess how students take into account the context of an image to provide its alternative text.
Topic: Complex Images
Describe mechanisms to provide additional descriptions for complex images. For example, the HTML elements figure
and figcaption
, or the WAI-ARIA attribute aria-describedby
. Emphasize that some additional descriptions may be provided by content authors. Relate these mechanisms to WCAG success criteria 1.4.5 Images of Text, and 1.4.9 Images of Text (No Exception).
Learning Outcomes for Topic
Students should be able to:
- mark up additional descriptions for images using one of the following techniques:
- HTML elements
figure
andfigcaption
- WAI─ARIA attribute
aria-describedby
- HTML attribute
longdesc
- HTML elements
- Style text decorations using CSS Transforms and CSS Fonts technologies instead of using images of text
- code mathematical expressions with the MathML language instead of using images of text
- categorize images based on the following types:
- textual
- complex
Teaching Ideas for Topic
Optional ideas to teach the learning outcomes:
- Explain that sometimes alternative texts are not enough to convey the information of an image. Discuss ways to provide additional descriptions for complex images and groups of images, for example the HTML elements
fig
andfigcaption
, and the WAI-ARIA attributesaria-describedby
or the HTML attributelongdesc
. For reference on how to describe complex images see the WAI website tutorials, Complex images. - Explain that many visual effects can now be achieved by using CSS Transforms and CSS Fonts technologies, instead of embedding an image file with text into a web page. For reference on using CSS3 properties to style text decorations, see the WAI website tutorials, Using CSS.
- Explain that the MathML language can be used to code mathematical expressions on the Web. Emphasize that screen reader support for MathML on the Web is growing, but other assistive technology users may need additional browser extensions to access contents in MathML. For reference on how to use the MathML language to code mathematical expressions, see the WAI website tutorials, mathematical expressions example.
Ideas to Assess Knowledge for Topic
Optional ideas to support assessment.
- Practical — Students are shown charts and graphics without descriptions and are asked to provide them. Assess how students provide adequate descriptions for complex images.
- Practical — Students are presented with a set of images of texts and are asked to code them using CSS Transforms and CSS Fonts technologies. Assess students’ knowledge of CSS Transforms and CSS Font technologies.
Ideas to Assess Knowledge for Module
Optional ideas to support assessment.
- Short answer questions — Students are asked about the mechanisms available for users of assistive technologies to move to next and previous image and to show all the images of a web page in an isolated list. Assess students’ knowledge of mechanisms of assistive technologies to move through images.
- Guided Quiz — Students are presented with a set of images in the context of a website and give their type and possible alternative text. Assess how students identify different types of images and provide alternative texts based on their purpose and context.
- Portfolio — Students add different types of images and graphics to the web site they are building. Assess how students code images and graphics and how they provide alternative texts based on their knowledge or with the help of other roles.
Teaching Resources
Suggested resources to support your teaching:
- WAI Web accessibility Tutorials — Shows how to develop web content that is accessible to people with disabilities.
- How People with Disabilities Use the Web — Provides stories of people with disabilities using the Web; describes types of disabilities and some of the barriers that people encounter using the Web; and introduces types of assistive technologies and adaptive strategies that some people use.
- WCAG — Address accessibility of web content on desktops, laptops, tablets, and mobile devices.
- WAI ARIA — Provides an ontology of roles, states, and properties that define accessible user interface elements and can be used to improve the accessibility and interoperability of web content and applications.
- HTML specification — The core markup language for the web, HTML, as well as numerous APIs like Web Sockets, Web Workers, localStorage, etc.
- Video Captions — Is one of the Web accessibility perspectives videos that show accessibility features and how they impact people with disabilities.