ALT tag and Image Descriptions

According to WebAIM, alternative text provides a textual alternative to non-text content in web pages. We will be discussing alternative text for images only, though the principles can be applied to media, applets, or other non-text web content.

Alternative text serves several functions:

  • It is read by screen readers in place of images allowing the content and function of the image to be accessible to those with visual or certain cognitive disabilities.
  • It is displayed in place of the image in browsers if the image file is not loaded or when the user has chosen not to view images.

It provides a semantic meaning and description to images which can be read by search engines or be used to later determine the content of the image from page context alone.

The key principle is that computers and screen readers cannot analyze an image and determine what the image presents. As developers, text must be provided to the user which presents the CONTENT and FUNCTION of the images within your web content.

Alternative text can be presented in two ways:

  • Within the alt attribute of the img element.
  • Within the context or surroundings of the image itself.

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How to add ALT text to images in Word or PowerPoint:

For Windows users

1. Open Word or PowerPoint document and right-click on the image
2. Select Format Picture
3. Click Layout & Properties icon on the left
4. Click Alt text
5. Enter image description

For MacOS users

1. Open MS Word or PowerPoint document and control-click on the image
2. Select Edit ALT text
3. Enter image description

How to add ALT text to images in Blackboard content editor:

1. Edit the page in Blackboard
2. Click on the image to select it
3. Click the person icon (accessibility checker) on the editor toolbar
4. Enter image description into "Provide Alternative Text" box

Note about descriptions for complex images:

When an equivalent alternative for a complex image, such as a chart, graph, or map cannot be limited to a succinct alt attribute (perhaps a couple sentences in length), then the alternative should be provided elsewhere. The alternative content can often be presented within the context of the page, such as in an adjacent data table. The alternative text for the image should still describe the general content of the image.

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