What it is
The alt attribute supplies a text alternative when an image cannot be seen, loaded, or understood visually.
Why it matters
Images are often blocked by default and screen-reader users may never perceive them. Meaning cannot depend on image loading.
How to implement
Describe the purpose of informative images in context. Use alt="" for decoration. Put essential calls to action in live text and repeat complex chart data in nearby text.
Common mistakes
- Repeating “image of” before a description.
- Using a filename or tracking identifier as alt text.
- Leaving out the attribute on spacer and decorative images.
Verification
Disable images, then read the message visually and with a screen reader. All actions and essential information must remain understandable.