Image alternative text, also called alt text, is a meaningful written description of a photo, image, GIF, animation, graph, etc. that screen-reading tools can read aloud to people who are blind or who have different sensory processing or learning abilities.
Well-written alt text accurately describes an image as well as communicates its purpose and context, to provide an accessible and functional user experience for everyone. Alt text also has important benefits for your website rankings. Search engines crawl alt text, so optimizing your images' alt text is an easy way to improve the user experience for all visitors.
Alt Text Best Practices
Below are a few best practices to help you write meaningful alt text.
- Describe the image in its context, and focus on the details the image adds to the text.
- Be specific, but try make the alt text fewer than 140 characters. Some screen readers will cut off once that limit is reached.
- Leave out phrases like "image of" or "picture of" in the description. They are repetitive because screen-reading tools identify images from the HTML source code.
- Avoid repeating information that's already covered in a caption or adjacent heading.
- Don't cram in SEO keywords. Search engines crawl alt text but dislike keyword stuffing.
- When an image includes graphs, formulas, or other important text, provide a transcript.
- Use an empty alt tag (alt="") for decorative images that don't contribute to greater understanding of the content. Using the empty alt tag hides decorate images from screen readers. Note: When uploading a decorative image on Digital Commons, select the "Decorative Image" checkbox. You don't need to add the quote marks ("").
Descriptive vs. Specificity
Bad Alt Text
This line of alt text technically follows the "be descriptive" rule, but it's too general. The image does show a lighthouse—more specifically, Bodie Island Lighthouse on North Carolina's Outer Banks. It's important to include specifics like that in alt text. Search engines need them to properly crawl the image, for example, if it's on a web page about North Carolina lighthouses.
Good Alt Text
Better alt text for this image might be:
alt="Bodie Island Lighthouse on North Carolina Outer Banks"
Depending upon the subject of your content, you might also mention the scenic landscape.