Images can do a lot of work in a course. They can explain a concept, show a process, provide evidence, set context, or simply make a page more inviting. Alternative text, often called alt text, helps make sure the meaning of an image is available not only to students who can see it.
But writing good alt text does not begin with describing everything in the picture. It begins with a simpler question: Why is this image here?
Who Benefits from Alt Text?
Alternative text, commonly referred to as alt text, is essential for people who use screen readers, including many blind and low-vision learners. A screen reader can announce the text alternative so that important information conveyed visually is also available in another form.
Alt text also helps in other situations. It can provide useful information when an image does not load because of a slow or inconsistent connection, when a content blocker prevents an image from displaying, or when someone is using an audio format of course content. For faculty and instructional designers, writing alt text can also prompt a useful design question: Does this image contribute something students need, or is it simply decorative?
Hear the difference
Ally can turn course materials into audio Alternative Formats for students. When an image has useful alt text, that description can become part of what the student hears. When alt text is missing, vague, or unhelpful, important information from the image may be lost.
Example 1: Missing and unhelpful alt text
- Missing Alt Text
- Unhelpful Alt Text
Example 2: Meaningful Alt Text
- Meaningful Alt Text
This is one reason accessible source materials matter: better-structured source content can produce higher-quality Alternative Formats for students.
Alt Text Is Not the Same as a Caption
A caption is visible to everyone and may provide context, explanation, attribution, or a figure label.
Alt text provides the text equivalent needed when a person cannot access the image visually.
Sometimes a caption or nearby text already communicates everything the image contributes. In that case, repeating the same information in the alt text may not help the reader. Depending on the image and context, marking the image as decorative can be the better choice.
Where Do You Need Alt Text?
Add a text alternative when a visual element communicates information a learner needs. Common examples include:
- Photos and illustrations
- Charts, graphs, and diagrams
- Images that contain meaningful text
- Important logos
- Images used as links, buttons, or other controls
Not every image needs a written description. If an image is purely decorative, or if the same meaningful information is already fully available in nearby text or a caption, marking the image as decorative may provide a better experience than making a screen reader announce redundant information.
Before Writing Anything, Ask What the Image Is Doing
- Why is this image here?
- What does a student need to know or do because of it?
Once you know the purpose of the image, writing useful alt text becomes much easier!
Different images do different jobs. Identifying that job first makes it much easier to decide what kind of text alternative is appropriate.
| Image type | What is the image doing? | Accessibility approach |
| Informative | Communicates information or meaning | Describe the information the learner needs. |
| Functional | Acts as a link, button, or other control | Describe what it does or where it goes. |
| Decorative | Adds visual interest without adding meaningful information | Mark it as decorative. |
| Complex | Communicates substantial information, such as a chart, graph, or diagram | Provide concise alt text plus a fuller text equivalent when needed. |
The key is that alt text is not one-size-fits-all. A functional image needs a different kind of description than a photograph, and a complex graph may need more than can reasonably fit in a short alt text field, while a decorative image can be marked as such.
Decorative Images
Not every image needs alternative text. A decorative image adds visual interest but does not communicate information that a student needs to understand the content. Examples might include a decorative divider, background images, or a generic stock photo that doesn’t add meaning to the lesson.
If removing the image would not change what a student needs to know: it’s likely decorative.
For decorative images, the goal is to mark the image as decorative so assistive technology can skip over it. This keeps screen reader users from having to listen to unnecessary descriptions and makes important content easier to find.
In Blackboard Ally
When Ally identifies an image that is missing a description, open the Accessibility score indicator to view Instructor Feedback. If the image is only decorative, choose the “Indicate image is decorative” option rather than adding alt text. Ally does not require an alternative description for decorative images.
This is also useful because it records the decision that the image does not contribute instructional meaning, rather than leaving an empty field that may look like an unfinished accessibility issue.
Ally also supports marking images inside PDFs as decorative through the Instructor Feedback panel when that remediation option is available. The updated PDF is then written back to your course.
Learn more about image descriptions and decorative images in Ally.
In Microsoft Word or PowerPoint
Word and PowePoint also let you explicitly identify visuals that are decorative.
- Select the image or visual.
- Right-click and choose “View Alt Text…”
- Toggle “Mark as decorative” to the on position.
When you designate an image as decorative, the alt text field becomes unavailable for text entry. If you change your mind and decide to describe the image, turn the decorative setting off.
When working on longer documents or PowerPoint presentations, you can leave the alt text panel open as you navigate through your document and select images one-by-one. This way you don’t have to right-click every image you want to mark decorative.
Another benefit in Office is that when a document or presentation is exported to PDF, visuals marked decorative are treated as “artifacts” in the PDF, which tells screen readers to ignore them.
Learn how to write effective alt text from Microsoft
A Quick Test to Help You Decide
Ask: If the image disappeared, would the student lose information, context, or the ability to complete an action?
If yes, the image probably needs meaningful at text or another text equivalent.
If no, it’s likely decorative.
Key Takeaway
Alt text is not about describing every aspect of an image. It’s about deciding what information the image contributes and making sure that information is available another way.
Coming in Part 2: We will look at how to turn that purpose into useful alt text, including what to describe, what to leave out, and why the same image may need a different description depending on how it is being used.
