Start with the image’s job
Alt text is a written alternative to an image. When a screen reader encounters an image, its alt text can convey information that a sighted reader gets by looking at it. The goal is not to describe every visible detail. It is to communicate what the image adds to the page.
Before writing, ask: Why is this image here? A photo might show how an object is used, establish a setting or simply add visual interest. The same photo could need different alt text in different articles. In a guide to using a self-service ticket machine, “Hand reaching for the large confirm button below the fare options” may be useful. In an article about a station renovation, the machine might be incidental; the image’s contribution could instead be the layout of the entrance.
Next, read the heading, caption and paragraphs around the image. Note what they already explain and what a reader would miss without seeing the image. That gap is the best starting point for alt text.
Let nearby text do its share of the work
Repeating a caption word for word rarely helps. If a caption says, “A volunteer demonstrates a raised garden bed at a community workshop,” alt text with the same sentence makes some readers hear it twice. Instead, describe a relevant detail the caption does not cover: “The bed sits at waist height, with open space beneath one side for a seated gardener.” Together, the alt text and caption give a fuller account without duplication.
Sometimes the surrounding text already supplies everything an image communicates. A decorative photo of leaves between two sections of a gardening article may not need a spoken description at all. In HTML, an empty alt attribute (alt="") tells assistive technology to skip it. That is different from leaving the alt attribute out, which may cause a screen reader to announce a file name or other unhelpful information.
Avoid making alt text so dependent on nearby text that it stops making sense. “As described above” does not identify an image’s contribution. A reader may navigate directly to the image, and the reading order may differ from the visual layout. Write a short description that can stand on its own while complementing the surrounding copy.
Describe information, not every pixel
For an informative photo, choose details that serve the article’s purpose: an object’s position, a person’s action or a visible difference that the text discusses. Compare “A room with people, tables, chairs and windows” with “Participants sit in a circle around a low table, leaving a wide route between the seats.” The second description helps explain an article about arranging a flexible meeting space.
Be careful with interpretations that an image cannot establish. “A frustrated customer struggles with an inaccessible kiosk” assumes an emotion and a cause. “A customer leans toward a kiosk screen mounted above their seated eye level” describes what is visible. If the article explains the access barrier, the two pieces of text can work together.
Charts and diagrams often need more than a compact label. Alt text can state the main takeaway, such as “Diagram showing three entrances connected to the central courtyard; only the east entrance has a step-free route.” Put detailed values, labels or instructions in nearby text or a data table when they matter. That lets readers examine the information rather than relying on one long image description.
Treat buttons and linked images as actions
An image used as a control has a different job from an image illustrating a story. For an icon-only button, the accessible name should tell people what the control does: “Search,” “Close menu” or “Download guide.” “Magnifying glass icon” describes its appearance but does not explain the action. Likewise, a linked image needs a name that communicates where the link leads, unless adjacent text in the same link already does that.
Consider a card with a photo, a visible title reading “Plan a step-free visit” and a link that wraps both. Giving the photo alt text of “Plan a step-free visit” may cause the link name to repeat itself. If the photo adds no essential information, empty alt text may be the clearer choice. If the photo shows an important feature that the title does not mention, a brief description can add value.
For logos, the organization or product name is usually more useful than a description of its colors and shapes. As with any linked image, check the complete link or button name, not just the alt text in isolation.
Test the result in reading order
A useful final check is to read the page as a sequence: heading, paragraph, image alternative, caption, next paragraph. Does each part add something, or does the same sentence recur? Would someone who cannot see the image understand the point it makes? If an image is decorative, would skipping it leave the meaning intact?
Keep alt text concise enough to follow in the flow of a page, but do not cut essential information just to meet an arbitrary word count. When a detailed explanation is necessary, place it in the article where everyone can use it. Good alt text is part of good editing: it gives an image a clear purpose and lets the rest of the page carry its share of the explanation.
