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Image Descriptions in Websites and Documents

Our last article explored alternative text (alt-text) descriptions of images, as part of universal design for the web. In this article, we will discuss image descriptions in websites and documents, a different way to make pictures perceivable to a variety of viewers.

Image Descriptions in websites and documents

Limits of Alt-text

Alt-text is a useful way to ensure that people who use screen readers can perceive images. However, alt-text has some disadvantages. For example, some programs limit the number of letters and numbers in alt-text. Therefore, content creators may not be able to fully describe detailed images, such as:

  • Maps
  • Graphs
  • Diagrams

In addition, programs that content creators use present alt-text in different ways. On one hand, websites and PDF files allow screen-reader users to scroll through alt-text. This navigation method gives people choice, the same way they can choose to scroll through the rest of the written document in different ways, such as:

  • Letter-by-letter
  • Word-by-word
  • Line-by-line

On the other hand, other programs present a piece of alt-text as if it were a single character. As a result, screen-reader users must listen to the whole piece of alt-text at once. The longer a piece of alt-text is, the harder it is to hear all of it at one time.

Furthermore, alt-text only appears to people who use screen readers. While screen-reader users certainly benefit from alt-text, some people who do not use screen readers may also find textual image descriptions useful. For instance, these descriptions might be useful to people who have other disabilities, such as:

  • Visual impairment
  • Visual processing disabilities
  • Intellectual disabilities
  • Learning disabilities

Moreover, many other people may benefit from access to images and text descriptions at the same time.

Image Descriptions

In short, alt-text is not the most suitable way to describe long images and make them accessible to a variety of people. Therefore, a best practice of universal design for the web is to create image descriptions for complex images. Image descriptions are visible to every reader of a website or document, not just people using screen readers. In addition, image descriptions can be long, and can also include formatting to help people navigate, such as:

Content creators can place image descriptions within a website or document, above or below the image. Alternatively, content creators can place image descriptions in a separate file.

When a content creator writes an image description, alt-text is not needed to describe the image. However, the content creator still needs to include one brief line of alt-text, to:

  • State what the image is
  • Alert readers that a description of the image is nearby

This alt-text is needed because images requiring descriptions are important images. However, other visual elements of websites or documents, called decorative objects, do not need alt-text. Our next article will discuss decorative objects.