Section 2.2: Creating Equivalent Text Alternatives, Part 1

Basic Things to Consider about ALT Text:

1. It should be short: 150 characters or less including spaces and punctuation.
2. It should make sense out of context; for example if read aloud by itself.
3. It should make sense in context; for example, if read aloud as part of the page.
4. It should contribute to the intelligibility of the page as an auditory experience.

Additional Notes about ALT Text:

• Screen readers typically announce when text is a link or a graphic. In many cases, you don't need to include that information in the ALT text.

When ALT text should be "silent"

At times ALT text may actually not contribute positively to the auditory experience of a page. When the page already contains a detailed description of an image, ALT text may be repetitive or unnecessary. Identifying or describing images that provide no meaningful content, such as decorative images, may only impede the access of a visually impaired reader to the content. The image must still have some kind of ALT associated with it, but in this case the ALT text should be empty (this is sometimes called “setting alt to null”). This makes screenreaders and talking browsers behave as if the ALT text isn't there, whereas the screenreader just reads the SRC attribute if the alt attribute is missing completely.

The HTML syntax would look like this:
<IMG SRC="http://www.somewhere.edu/images/spacer.gif" ALT="">

Examples of Equivalent Alternative text

This image from the National Museum of American History home page is used as a link to information about the Treasures of American History. The ALT text captures the role of the image.

The ALT text is "Treasures of American History opens November 17 at the National Air and Space Museum."

Note: A good rule of thumb is that in most cases the text within an image probably needs to be included in the ALT text.

This image from one of the collections pages of the National Museum of American History is used to help describe one of the items in their collection, the Kodak Petite Camera. In this case the page includes a thorough description of the item and the role of the image is to provide and support the content.

The ALT text for this image is "Kodak Petite Camera".