How to write useful image alt text

Alternative text is a text replacement for an image in its context. That last phrase matters. The same image can need different treatment when it explains a subject, decorates a page, or acts as a link. Start with the W3C image decision tree rather than a target word count.

Describe the visual information a reader needs

If the image disappeared, what information or function would be lost? A close-up of a leaf in a botanical identification guide may need a description of its distinguishing features. The same leaf used behind an unrelated section heading may be decorative and need an empty alt attribute.

For Stockphoto.now’s botanical image, “Water droplets on a green monstera leaf against darker foliage” is a concrete description of visible content. It does not need a list of potential uses such as sustainability, wellness, marketing, and business.

Write alt text for the image’s purpose

For an informative image, describe the important visual information concisely. For a functional image, communicate what the control or link does. For a decorative image, use an empty alternative so assistive technology can skip it. Complex charts may need a short alternative plus a longer explanation in the surrounding page.

A linked thumbnail beside a visible title can become repetitive if both announce identical text independently. Consider the accessible name of the whole link. A download icon needs a functional label such as “Download the coastal image,” not a visual description such as “Downward arrow.”

Avoid unsupported claims in image descriptions

Do not infer a person’s identity, emotions, disability, or location from appearance when that information is not established. Describe visible actions and surroundings where they matter. An imagined coastal scene should not be labeled as a verified photograph of a specific destination.

When AI generation affects the reader’s interpretation, disclose it in visible nearby text as well. An alt attribute is not a substitute for a clear editorial label that everyone can see.

Match alt text to the surrounding content

If the caption already provides a detailed explanation, the alternative can focus on the visual information the caption does not replace. Do not use the same paragraph in the caption, alt text, and nearby body merely to repeat keywords. Repetition makes the page harder to navigate.

A reasonable test is to read the page aloud with the image descriptions inserted where the images occur. Does the flow still make sense? Do linked cards announce useful destinations? Are decorative flourishes interrupting the content?

Test image descriptions in the real interface

• Confirm every image has the appropriate alt attribute.
• Check that linked images have a meaningful accessible name.
• Keep decorative alternatives empty.
• Use visible labels for material AI disclosures.
• Test keyboard focus and the reading order around image controls.

For visual layout decisions, see composition and copy space. Contributors can apply these principles in the submission and review guidelines.