The rule
Provide "additive" descriptions for informative images that complement the surrounding copy.
Why it matters
Alt text allows people with vision loss to understand the purpose of an image through a screen reader. Without it, the device may read a meaningless file name, which frustrates users and blocks access to information.
How to apply it
- Keep descriptions to one or two short, straightforward sentences.
- Use an empty alt attribute (
alt="") for decorative images so assistive tools know to skip them. - Don't start with "image of" or "photo of" — screen readers already announce the element type.
- For images that function as links, describe the destination, not the image itself.
Example
Before and after
Avoid
alt="Photo of a cat."
Better
alt="A ginger cat sleeping in a sunlit window."
Tensions and exceptions
If a visible caption or nearby body text already fully describes everything in the image, the alt text should be empty to avoid redundancy for the user.