Writing alt-text

Published on: 04/02/2025 · Last updated on: 17/04/2026

What to do

You need alt‑text whenever you use:

• Photos
• Diagrams
• Charts or graphs
• Images containing text

Why do it?

Alt‑text is a short text description that conveys the meaning of an image for people who cannot see it. It ensures that students using screen readers can access the same information as sighted users. It also provides a fallback if an image fails to load.

How to add alt-text to an image

Adding alt-text in Word, PowerPoint and Microsoft Office

1. To add alt-text to any image in Microsoft Word or PowerPoint, right click on the image,
2. then select “Edit Alt-text” from the dropdown menu
3. enter the description into the box. 

Adding alt-text in Moodle

When inserting an image, enter the description in the Alt text field. To edit existing alt‑text, select the image and click the Image button.

How to write effective alt-text

Good alt‑text is:

• Contextual – describe what matters in this specific learning activity.
• Concise – usually 1 – 2 sentences.
• Objective – describe what is visible, not how to interpret it.
• Non‑redundant – doesn’t repeat nearby text

Avoid:

• “Image of…”
• Decorative detail
• Opinions or assumptions

If the image were removed, would the alt‑text still communicate its meaning?

Here are some useful resources on writing alt-text with examples

• WebAim Guide to Writing Effective Alternative Text
• Accessible Images Home (Penn State) 

What is the difference between a caption and alt-text?

A caption appears next to an image and supplements an image for all users. It could contain a title, overview, context, copyright/source information or extra information about the image.

Alt-text replaces the visual aspects of an image through a text description for users who can’t see the image. A caption can be useful for readers, but can never replace the need for alt-text.

How to support complex images

Many diagrams or graphs in teaching can’t be fully described in a short alt‑text. It is still essential to provide alt-text for images, but some additional considerations may need to be put in place to makes things accessible.

The recommended approach to alt-text is outlined Describing complex images resource:

1. Can teaching points be described in a few sentences?​ If so, just use normal alt-text.
2. Does nearby text already explain it? If yes, use the alt-text to signpost the text description (e.g. “see body text for description”).
3. Is the information available and digitally accessible elsewhere (e.g. ebooks, audio files, websites)?​ If yes, use the alt text and a caption to signpost to an alternative format (alt text = “see caption for link to alternative format”)
4. Can AI tools make a good description of the main teaching points (e.g. Microsoft CoPilot)?​ If yes, edit for accuracy, and then upload this separate online description to Moodle and reference to it with alt-text and caption.
5. Use the suggested Alt Text formula outlined in Suggested workflows (Describing complex images).

Also see our guidance on How to create accessible figures and diagrams.

Using Microsoft Copilot to Help Write alt‑text and Long Descriptions

Microsoft Copilot can help draft alt‑text or a longer description when you paste an image into the chat. It can identify shapes, text in the image, labels and basic relationships. This can be a useful starting point for:

• Charts and graphs
• Diagrams or flowcharts
• Images containing embedded text

Always review the result, as AI‑generated descriptions may contain errors or miss key teaching points.

How to use Copilot

1. Copy the image (or take a screenshot)
2. Paste it into Copilot
3. Use a clear prompt (see below)
4. Edit for accuracy, context, and tone before adding it to your document or Moodle.

Suggested prompt:

Please describe this image for accessibility. First write concise alt-text (1–2 sentences). Then provide a longer description listing any labels, structure, or text visible. Describe only what is present, no interpretation.

When to set an image as decorative

Mark an image as decorative if it adds no new information—such as a visual flourish or repeated iconography. Decorative images should be correctly flagged so screen‑reader users can skip them.

Decorative Images ((WAI) | W3C) provides guidance and examples on when it’s appropriate to mark something as decorative.

Alt text guidance for AI‑generated images

Research with screen reader users shows that AI‑generated images need slightly different alt‑text treatment to ensure they are accessible and trustworthy (Das 2024, From Provenance to Aberrations: Image Creator and Screen Reader User Perspectives on Alt Text for AI-Generated Images).

• Avoid prompt‑style jargon unless it meaningfully helps the reader (e.g. artistic styles relevant to teaching).
• Describe what’s actually visible, not what you intended or how it makes you feel. Avoid subjective language unless it’s clearly supported by visible cues.
• Say it’s AI‑generated (where relevant): e.g. “AI‑generated image” or “Image created using an AI tool.”
• Use cautious wording if something is unclear: “appears to be…”, “looks like…”
• Mention the image type if it’s not a photo (illustration, concept art, painting, diagram).
• Include odd, incorrect, or distorted details (e.g. unclear text, extra limbs) if they are noticeable and may be important to understanding the image.

How to spot alt-text issues

• Use the Microsoft Accessibility Checker (see later Checking your content section) to find images with missing alt-text within you files (Word, PowerPoint and Excel).
• Use Accessibility+ Toolkit to find and fix issues with missing alt-text on Moodle.

Additional support

• Improve image accessibility in PowerPoint (including for diagrams made of groups of shapes)
• Accessible Figures Guidance – University of Bath Teaching and Learning Hub.
• The DIAGRAMcenter.org have a series of examples sorted by figure type: for example bar graphs, line graphs,  relational diagrams with multiple start points/paths, etc.