Classify the image first
Context matters more than describing every visible detail. Empty alt is different from a missing attribute. For a chart, also make its data and relationships available as text or a table.
| Role | Text alternative | Useful complement |
|---|---|---|
| Redundant decoration | alt="" | Nearby text is sufficient. |
| Simple information | Brief contextual description | Avoid unrelated added keywords. |
| Image-only link | Destination or action | The link name must make sense. |
| Complex chart | Subject and main message | Provide the data and relationships in text. |
Check the actual experience
- For an image-only link, describe the destination or action. If sufficient link text already exists, avoid repeating it.
- Do not put essential instructions only in title: access through keyboard, touch and assistive technology is unreliable.
- Check labels in each language and the journey without images. Optimize dimensions and loading without automatically delaying the main visual.
Connect visibility with verified rights
A filename or markup does not guarantee indexing or ranking. Declare a license only after checking rights and retain required credits. Clearly identify synthetic illustrations rather than presenting them as documentary evidence.
Primary references
- W3C WAI — An alt Decision Tree [EN]
- W3C WAI — Functional Images [EN]
- MDN — title attribute [EN]
- Google Search Central — Image SEO [EN]
Alternative text depends on the image’s use
Descriptive alt text is not automatically the right choice. Redundant decoration can have empty alt; a linked image should communicate its destination; a complex chart also needs detailed description. Review the image in its actual page context.
- Classify decoration, information and function before writing.
- Put diagram relationships in nearby text or a table.
- Avoid keyword lists and describing fictional scenes as real evidence.
Primary reference: W3C WAI — An alt Decision Tree. Related method: read the practical guide.