[Draft] Module 3: Images and Graphics

• Prerequisites for Students
• Basic knowledge of:
  • HTML img element
  • HTML picture element
  • CSS Specifications

• 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
  • CSS Specifications
  • ARIA img role
  • WAI-ARIA attributes aria-label, aria-labelledby, and aria-describedby
  • Figure and figcaption elements
  • In-depth knowledge of Prerequisites for Students

Explain that simple images and graphics, such as informative, textual, and decorative, only require a short text alternative to describe them. Mention scenarios where text alternatives allow people to 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 attributes alt, title, aria-label, or aria-labelledby
• explain what simple images, such as informative, textual, and decorative, mean in the context of Web accessibility
• explain how text alternatives are read aloud by text-to-speech technologies
• explain how text alternatives 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 text alternative since that would be separately announced via the HTML element img. Mention that when an image is decorative, the value for the alt attribute should be empty (“”), and, whenever possible, the image should be included in the web page using CSS instead of the HTML element img. Examples of how to use alt to code text alternatives are provided in techniques H2: Combining adjacent image and text links for the same resource and H37: Using alt attributes on img elements.
• Demonstrate the use of other ways to convey text alternatives, such as the HTML attributes title, aria-label, or aria-labelledby. Explain that these may not be well supported by old browsers and assistive technologies. Examples of how to use aria-label and aria-labelledby to provide descriptions for images are provided in techniques ARIA6: Using aria-label to provide labels for objects and ARIA10: Using aria-labelledby to provide a text alternative for non-text content.
• Define informative, textual, and decorative images. Show examples of each, such as product prices, ornaments, or small pieces of textual information coded as an image. Show the same image in different web pages and explain that an image can belong to different types depending on the context. Descriptions of informative and decorative images are provided in the WAI tutorials on Decorative Images and Informative Images.
• Demonstrate the use of voice commands, keystrokes, and gestures provided by speech and mainstream technologies to navigate web pages through images. Explore advanced functionality that some tools provide, such as presenting all images in a list where users can select the image they are interested in. Examples of how people with disabilities interact with the Web are provided in 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 text alternatives. Emphasize how essential information is often missed due to the lack of text alternatives.
• Explain that text alternatives are one of the techniques used by search engines to determine what an image is about. Indicate that the more accurate an text alternative is, the better its image 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 text alternatives for images. Assess students’ knowledge of the different coding techniques to provide text alternatives for images.
• Practical — Students provide text alternatives for a given set of 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 text alternative for each. Assess how students take into account the context of an image to provide its text alternative.

Explain that functional images, such as images in links and buttons, provide functionality. Relate functionality of the image to its adjacent text.

Learning Outcomes for Topic

Students should be able to:

• code functional images using the HTML attributes alt or adjacent link text
• write text alternatives for button images, link images, and image input types that describe the action these images are carrying out
• explain what functional images mean in the context of web accessibility

Teaching Ideas for Topic

Optional ideas to teach the learning outcomes:

• Explain that functional images serve to initiate an action, rather than to convey information. For an explanation of what a functional image is, see the WAI tutorials on Images Concepts.
• Show examples of button and image input types, such as those for printing or saving a document. Explain that their text alternatives need to refer to the action that the image conveys. Examples of several text alternatives for functional images are provided in the WAI tutorials on Functional Images.
• Show examples of adjacent link or button texts that may influence the text alternative for a functional image. Explain that when the adjacent text conveys the action performed by the image, a null text alternative should be provided.

Ideas to Assess Knowledge for Topic

Optional ideas to support assessment:

• Short Answer Questions — Students are asked what a functional image is. Assess students knowledge of what a functional image is.
• Practical — Students are presented with functional images with and without surrounding text and are asked to provide text alternatives accordingly. Assess how students provide text alternatives for functional images based on context.

Explain that complex images, such as charts, diagrams, and infographics, provide rich information and require longer text alternatives to describe them. Discuss mechanisms to provide additional descriptions for complex images. For example, the HTML elements figure and figcaption, or the WAI-ARIA attribute aria-describedby. Mention that providing descriptions for a complex image is a shared responsibility among different team members: content authors, designers, and developers. 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 and figcaption
  • WAI-ARIA attribute aria-describedby
  • HTML attribute longdesc [primarily supported in eBook publication]
• style text decorations using CSS Transforms and CSS Fonts technologies instead of using images of text
• code mathematical expressions using the MathML language instead of using images of text
• categorize images based on the following types:
  • textual
  • complex
• summarize related requirements for authors to write meaningful text alternatives for textual and complex images

Teaching Ideas for Topic

Optional ideas to teach the learning outcomes:

• Discuss ways to provide additional descriptions for complex images and groups of images such as charts, diagrams, or screen shots of materials that are intended to be read as text. For example, the HTML elements figure and figcaption, the WAI-ARIA attribute aria-describedby or the HTML attribute longdesc. Mention that longdesc may not be well supported by some browsers or assistive technologies. Examples of how to describe complex images are provided in the WAI tutorials on Complex images and images of Text.
• 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 people using assistive technology may need additional browser extensions to access contents in MathML. Examples of how to use the MathML language to code mathematical expressions are provided in the WAI tutorials on mathematical expressions.
• 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. Examples of how to use CSS3 properties to style text decorations are provided in the WAI tutorials on Using CSS.

Ideas to Assess Knowledge for Topic

Optional ideas to support assessment:

• Practical — Students are asked to code descriptions for a set of given charts and graphics. Assess how students code descriptions for complex images.
• Practical — Students are presented with a set of images of text and are asked to code them using CSS Transforms and CSS Fonts technologies. Assess students’ knowledge of CSS Transforms and CSS Font technologies.