You’ve scanned your website for accessibility issues, and you’ve received a warning: Some of your images have the same alternative text (also called alt text). Why is that a problem, and how can you fix it?
Duplicate alt text isn’t always a problem, but it’s a potential sign that you’re misusing the HTML alt attribute. Some automated accessibility checkers will flag the issue for human review; others might ignore it entirely.
What causes a duplicate alt text warning?
Accessibility tests may define “duplicate alt text" slightly differently. Generally, the term means that the alt attribute of an image is identical to another image’s alt attribute.
However, some testers will also present a warning if the alt attribute is identical to any text near the image on the page. A common example: The image alt attribute might be identical to the image’s caption.
Is it a problem if several images have the same alt text?
Yes, in most cases. The purpose of a text alternative is right there in the name: It describes the content and context of an image to provide nonvisual users with an equivalent experience.
If two images serve an identical purpose, it’s reasonable to use the same alt text to describe both of them. Of course, this is rare — very few web pages include the same image multiple times, unless that image is purely decorative (in which case, the best practice is to use an empty or “null" img attribute).
Related: How Do I Know If an Image Needs Alt Text?
Is it a problem if an image's alt attribute is identical to its caption?
Yes. Screen readers (software that outputs text as audio or braille) will announce both the caption and the alt attribute, which is unnecessarily repetitive.
Unless you’re intentionally repeating information for a specific effect, the best practice is to keep the caption and use a null img attribute.
Related: Should You Include Alt Text for Pictures with Captions?
How does duplicate alt text impact users with disabilities?
As we’ve discussed, duplicate alt text creates noise for screen reader users— in this context, “noise" means content that results in repetitive or unnecessary output.
To get a sense of how this affects the user experience, imagine that a friend is telling you a story. He describes his car in great detail — then describes it again. Then, he describes it a third time. Are you still interested in hearing the rest of the story?
Clear, concise content is important for accessibility. By eliminating repetitive alt attributes, you’re substantially improving the experience for assistive technology users.
Related: Why Repetition Is Frustrating for Screen Reader Users (And How to Help)
Does duplicate alt text violate WCAG?
The Web Content Accessibility Guidelines (WCAG) requires text alternatives for all non-text content (with limited exceptions). Those text alternatives must provide a sufficiently equivalent experience for nonvisual users.
WCAG doesn’t specifically prohibit duplicate alt text. However, repetitive alt attributes could conceivably violate the guidelines if the descriptions don’t accurately describe the images — and more importantly, the repetition is annoying to human users.
How can I determine whether duplicate alt text is justified?
Unfortunately, software can’t tell you whether duplicate alt text is truly an issue for real-life users. You’ll need to review the warning and ask questions:
- Does the image have a caption? If so, use a null alt attribute.
- Is the image described clearly in on-page text? If so, use a null alt attribute.
- Do two different images have identical alt text? If so, change at least one of the attributes to explain the differences between the images.
- Do two identical images have identical alt text? If so, the “duplicate alt text" warning isn’t a problem — but if the images are purely decorative, you should use a null alt attribute.
- Are you using a “default" alt attribute for all new images on your website? If so, stop! Alt text needs to be descriptive of the image to be useful (and to fulfill WCAG).
Finally, remember that automated accessibility testers are intended to support human-led audits — they aren’t a complete solution to accessibility compliance.
At the Bureau of Internet Accessibility and AudioEye, we believe that the most effective path to compliance is a hybrid approach. By pairing powerful automation with expert-led testing and remediations, we provide organizations with sustainable strategies for compliance.
To learn more, send us a message to connect with a subject matter expert or get started with a free website accessibility scan.
