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Section 508 ICT Testing Baseline

6. Images

Accessibility Requirements

  • WCAG2 SC: 1.1.1. Non-Text – All non-text content that is presented to the user has a text alternative that serves the equivalent purpose, except for [specific] situations.
  • WCAG2 SC: 1.4.5 Images of Text – If the technologies being used can achieve the visual presentation, text is used to convey information rather than images of text except for [specific situations].
  • WCAG2 SC: 4.1.2 Name, Role, Value – For all user interface components (including but not limited to: form elements, links and components generated by scripts), the name and role can be programmatically determined; states, properties, and values that can be set by the user can be programmatically set; and notification of changes to these items is available to user agents, including assistive technologies.

Test Method Rationale

All meaningful and decorative images must be evaluated. Tests for certain image types are specified.

Limitations, Assumptions, Exceptions

  • Commonly used image formats include .jpg, .png, .svg, .gif, .tiff, .bmp. Other graphic formats are also in use and should be considered for this test.
  • Decoration, Formatting, Invisible: If image is pure decoration, is used only for visual formatting, or is not presented to users, then it is implemented in a way that it can be ignored by assistive technology.
  • CAPTCHA: If the purpose of the image is to confirm that content is being accessed by a person rather than a computer, then text alternatives that identify and describe the purpose of the image(s) are provided, and alternative forms of CAPTCHA using output modes for different types of sensory perception are provided to accommodate different disabilities.
  • Images of text which are essential to the information being conveyed are exempt from SC 1.4.5. Logotypes (text that is part of a logo or brand name) are considered essential.
  • The definition of image of text contains the note: “Note: This does not include text that is part of a picture that contains significant other visual content.” Examples of such pictures include graphs, screenshots, and diagrams which visually convey important information through more than just text.
  • Equivalent descriptions for an image within page text could allow an image to be considered decorative. However, this does not necessitate removal of any accessible text attributes from the image.
  • While a longdesc attribute has been used historically to provide extended description for images and is listed as a sufficient technique in WCAG (H45), the technique is not currently well supported for accessibility and is not part of the accessible name or accessible description computation for an image; therefore, this Baseline does not accept the technique.
  • The combination of an element’s accessible name and accessible description is its text alternative.

6.1 Test Procedure for Meaningful Images

Baseline Test ID: 6.1-MeaningfulImage

Identify Content

Identify any image that conveys information (include images of text; functional images used to initiate action, convey meaning, or prompting a response; image maps, etc.).

Test Instructions
  1. Check that the text alternative (combination of the accessible name and accessible description) is not empty. [SC 1.1.1]
  2. Check that the non-empty text alternative (combination of accessible name and accessible description) provides an equivalent description. Numerous attributes contribute to the computation of the accessible name and accessible description. Refer to HTML Accessibility API Mappings 1.0 for img. [SC 1.1.1]
    1. Descriptions of the image that are provided by page content must be programmatically associated.
    2. When an image is updated to convey a new meaning, check that its text alternative is updated at the same time. [SCs 1.1.1 and 4.1.2]
  3. Check that the ARIA role is NOT "presentation".
  4. Check that the ARIA role is NOT "none".
  5. Check that aria-hidden is NOT set to "true".
Test Results

If any of the above checks fail, then Baseline Test 6.1-MeaningfulImage fails.

6.2 Test Procedure for Decorative Images

Baseline Test ID: 6.2-DecorativeImage

Identify Content

Identify any decorative image that is pure decoration, is used only for visual formatting, or is not presented to users.

Test Instructions

Check that at least one of the following is true [SC 1.1.1]:

  1. The ARIA role is "presentation".
  2. The ARIA role is "none".
  3. The aria-hidden is set to "true".
  4. The text alternative (combination of accessible name and accessible description) is empty (e.g. ""). Numerous attributes contribute to the computation of the accessible name and accessible description. Refer to HTML Accessibility API Mappings 1.0 for img.
  5. The image is inserted via CSS (e.g., using a background image).

Test Results

If all of the above checks fail, then Baseline Test 6.2-DecorativeImage fails.

6.3 Test Procedure for Captchas

Baseline Test ID: 6.3-Captcha

Identify Content

Identify any CAPTCHA designed to determine if content is being accessed by a person rather than a computer.

Test Instructions
  1. Check that the text alternative (combination of the accessible name and accessible description) is not empty. [SC 1.1.1]
  2. Check that the non-empty text alternative (combination of accessible name and accessible description) identify and describe the purpose of the CAPTCHA. [SC 1.1.1]
  3. Check that alternative forms of CAPTCHA are provided, at a minimum, for users without vision and users without hearing. [SC 1.1.1]
Test Results

If any of the above checks fail, then Baseline Test 6.3-Captcha fails.

6.4 Test Procedure for Images of Text

Baseline Test ID: 6.4-ImageText

Identify Content

Identify any images of text, except where a particular presentation of text is essential to the information being conveyed (e.g., logotypes or text that is part of a logo or brand name).

Test Instructions

  1. Check that using text cannot achieve the same visual presentation and effect as images of text. [SC 1.4.5]
  2. Check that the image of text can be visually customized to a user's requirements. [SC 1.4.5].
    For example, web content allows users to specify font, size, color, and background settings, and all images of text are then provided based on those settings.

Test Results

If any of the above checks fail, then Baseline Test 6.4-ImageText fail.

Advisory: Tips for streamlined test processes

WCAG 2.0 Techniques

Contact the ICT Baseline Working Group


Related Projects

The Baseline Alignment for Web is being developed to aid in determining if a test process aligns with the ICT Baseline for Web.