Image alt text
Images make your guide engaging and pleasant for many visitors. However, images are visual, so they can be a barrier to accessibility.
One way of making images more accessible is to add alternative text (commonly shortened to "alt text"). Alt text is one to three short sentences that describe the image. Alt text gives visitors who are blind or have low vision the same meaning that the image gives sighted visitors.
What is alt text?
Alt text is a short written description that replaces the experience of seeing an image. Alt text puts the image’s purpose, context, and key visual information into words. This lets people understand and navigate the screen with a different sense, like hearing or touch.
Alt text must be short and objective. Don't use alt text for subjective or interpretive information, or for any information that a sighted visitor can't get by looking at the image. If you want to provide more interpretive or evocative information about an object, space, or artwork, consider creating a verbal description tour.
Primary audience
People who are blind or have low vision.
Experience
Alt text does not appear as text on a screen. Alt text is read out loud by a screen reader or converted to a braille display to improve or replace the experience of seeing an image.
Writing alt text
We worked with experts in art and accessibility to develop an AI tool that generates alt text for your image. You can use this tool to generate your alt text, or write your own. It’s important that you add alt text to all images in your guide.
Alt text isn't completely new content. Instead, remember that alt text gives the same information that the image itself conveys. This way, sighted and non-sighted visitors can have an equivalent experience of the same content.
- Don’t repeat the image caption.
- Be concise.
- Most sources suggest keeping alt text to 125 characters or less (one to three short sentences). Remember that someone listens to the alt text to understand the basic information on the screen, as if they were looking at the screen quickly. They don’t want to listen to a long paragraph.
- Be objective.
- Do not include information about the historical context, artist, or technique unless such details would be obvious to a sighted user.
- Put the most important information first, so someone can skip the rest if they need to.
- If an image includes text, include the exact words in the alt text.
- Avoid phrases like “an image of” and “a picture of.”
- Screen readers automatically announce the object as an image, so these phrases repeat information.
Inappropriate alt text can be as much of a problem as no alt text, because it can confuse visitors or give them too much unnecessary information.
Alt text in context
What’s the difference between image alt text, image caption, item description, and verbal (audio) description?
In your guide, each of these elements has its own purpose. Together, they can give visitors a complete and accessible experience.
- Image alt text: Strongly recommended. Specific to an individual image. The text equivalent of the image itself. Does not provide any interpretive information. Does not appear on the screen; is read out loud by a screen reader.
- Image caption: Required. Specific to an individual image. Usually identifies the image to meet legal attribution requirements, but your organization can choose to include more information. Appears onscreen, directly below the full screen image.
- Item description: Strongly recommended. Applies to an entire item. Provides more or interpretive information about the subject of the image (for example, the work of art or object).
- Verbal (audio) description: Optional. Applies to an entire item. An audio file that uses interpretive language to provide a detailed description of the object. Verbal descriptions are recorded by a human and include much more detail than would be appropriate for alt text. For more, see Verbal description tours.
Take this image as an example:
- Image alt text: A bronze globe covered in carved constellations rests on a blindfolded reclining figure on a marble base.
- Image caption: Paul Manship, Celestial Sphere, 1934
- Item description: An avid stargazer, Manship was fascinated by the constellations, the signs of the zodiac, and their relationship to classical mythology. He used those motifs to create the Celestial Sphere. A 12-foot diameter version of Celestial Sphere is featured in the Woodrow Wilson Memorial of the Garden of the United Nations, in Geneva, Switzerland. In that version, bronze was used for the much larger base, instead of marble.
- Item verbal description: In this piece, Manship laid carved bronze figures of constellations over the hollow frame of the globe. Under each figure is a banner that bears the constellation's name. The figures are painted gold, and the frame and supporting structure of the globe are a dark patinated bronze. The globe is supported by a reclining female figure with a long ribbon covering her eyes like a blindfold to signify the unknown.
Examples
Remember that the image's context is critical when it comes to writing strong alt text. The following section provides a few examples of how context can impact alt text.
Subject: Art
Context: A photograph of a work of art in an item dedicated to that work. The audience should get a short, general sense of what the work of art looks like.
Alt text: Against a dark background, a woman wearing a blue and yellow head wrap looks over her shoulder. A large pearl earring reflects the light.
Subject: Person
Context: An image used in an exhibition of famous authors. The audience does not need to know all the details.
Alt text: Author Toni Morrison at a desk in her upstate New York home
Subject: Plant
Context: A photograph of a living botanical specimen from an organization’s garden or grounds, provided for informative and aesthetic purposes, instead of for scientific purposes.
Alt text: A macro photograph of a cherry tree in bloom with small, light pink blossoms.
Subject: A building, room, or other physical space
Context: The main image for an item used that gives “About Us” information.
Alt text: The museum's lobby and entrance to Gallery 1.
If you use this image in an item that introduces an exhibition space or gallery, the alt text should include different, more relevant details. The same is true if you use it to show something specific about the building's architecture. For example, we might mention the wood paneling, the pattern on the floor, or the layout, depending on what's most relevant.
Resources
General
- AI Alt Text
- Alternative Text (WebAIM)
- Images Tutorial (Web Accessibility Initiative)
- Alt-texts: The Ultimate Guide (Axess Lab)
- Image Descriptions (Diagram Center: A Benetech Initiative)
Alt text for art
- How Museums are Making Artwork Accessible to Blind People Online (ArtNews)
- Alt Text and Accessibility: Describing the Act of Looking (RISD Museum)
- Digital Accessibility (Sam Fox School of Design & Visual Arts at Washington University in St. Louis)
- Guidelines for Image Descriptions (Cooper Hewitt)
- What is “equivalent” text alternatives for artistic and cultural visual content? (Axe-con 2024)
- Alt-Text for Art and Design Images (Sam Fox School of Design & Visual Arts at Washington University in St. Louis)
- How to Write Alt Text for Amateur Art (Veronica Lewis (Veronica with Four Eyes))
Alt text for architecture
- Alt-Text for Architecture Images (Sam Fox School of Design & Visual Arts at Washington University in St. Louis)
- The Description of Architectural Drawings (The Getty Museum)
- How to Write Image Descriptions for Buildings and Architecture (Veronica Lewis (Veronica with Four Eyes))
Verbal descriptions
- Guidelines for Verbal Descriptions (Art Beyond Sight)