Alternative text | Digital Museums Canada

Alternative text

Conveying visual information as text.

What to know about text alternatives

Text alternatives, or alt-text, convey the purpose of an image (pictures, illustrations, charts, etc.) through words. Alternative text allows visually impaired users to hear the description read aloud with a screen reader, provides context when images are disabled or fail to load, and are used by search engine crawlers to identify, categorize, and associate the images with key words.

Good alternative text should describe the image to explain any information conveyed by the image needed to fully understand the web page’s content. Understanding of the content should be equal whether a user is looking at the image or reading the alternative text.

What to check

  • Ensure there is alternative text for each image on the website.
  • If an image is purely decorative, this does not apply. For example, a green square that is a part of the page’s design. In this case, ensure that the image is identified but the alt tag is empty, so screen readers do not read through it.
  • Since some screen readers cut alt text descriptions at 125 characters, ensure the short text sufficiently describes the image in the least amount of characters.
  • The alt text should take the context of the page into account and not repeat the information in a caption or associated to the image on the page.
  • If the alternative text is not sufficient, ensure a longer description is available nearby.
An image on a website has an arrow pointing to it and is used as the example described below.

Highlighting an image from the Tides to Tins virtual exhibition. Alt-text for the image: “A figure standing on a riverbank outside the walls of a wooden fort. Handwritten text at the bottom of the photo says: “Hudson Bay Post- Langley- 1862.”

Web page screen capture with arrow pointing to the page banner.

Highlighting the banner image from the Living Tradition virtual exhibition. Alt-text for the image: “Two weather dancers in white wool and fur regalia, fur headdress and face paint, standing in a forest.”