Alternative Text
Alternative text or ALT tags are invisible descriptions of images which are read aloud by screen readers typically used by blind users. Adding alternative text allows authors to include images, but still provide an alternative text based format of the content.
Adding alternative text for images is one of the main principles of web accessibility. It is also often one of the most difficult to properly implement determining appropriate, equivalent, alternative text is often a matter of personal interpretation.
Example of Alternative Text
Consider this painting of George Washington at Valley Forge (Picture from Library of Congress).
When thinking of alternate text, the task would be to consider WHY the image is included. Is it within a history course? A course on climatic history? Is the point of the image to show how soldiers were dressed or that Lafayette was at Valley Forge?
The answer could affect how you write the alternative text.
Possible alternative text for George Washington Painting:
- "George Washington at Valley Forge" (most succinct)
- "George Washington and Lafayette on horseback talking to soldiers in snow at Valley Forge" (more detailed)
- "Valley Forge in winter. The landscape is snow covered and soldiers are sitting by the open road with a camp fire." (emphasizing climate)
Hint on long descriptions: If a description is very technical it may be worth including it in the main text so that all readers can benefit as well as those only receiving the alternative text.
Decorative Images Alternative Text
A decorative image is one used to enhance the mood of a document, but not to convey actual information. Decorative images can include tool bars, clip art, photographs to add "color" and repetitions of a logo. Even the picture of George Washington above could be considered decorative if it is not directly connected to events at Valley Forge, but part of a more generic page.
Decorative images still require alternative text, but can be labeled as a "decorative image."
More information:
For more information on alternative text and descriptions, please visit WebAIM’s Alternative Text page.