PվƵ aims to assist authors in crafting effective Alternative Text (Alt Text) for images to support accessibility for visually impaired users. Good Alt Text clearly explains the key elements and purpose of an image in its specific context, providing the same information that sighted users would gain.
While writing Alt Text can be somewhat subjective, the goal is to provide a clear, meaningful description that makes sense and conveys the necessary information to visually impaired users.
Mistaking Captions for Alt Text: Alt Text is different from a caption. A caption usually provides extra information not shown in the image. For example, a caption might read “A group of friends celebrate a birthday.” This does not specify if they are blowing out candles on a cake, opening presents, or playing games.
Adding Extra Information: Alt Text should describe only what is in the image without adding extra details. Including additional information can confuse visually impaired users or give them unfair advantages by providing information other users do not have. For example, do not assume a person holding a book in a classroom is the teacher unless it is clear in the image.
Describing Decorative Images: Do not write Alt Text for images that are purely decorative. If the image is just for decoration and does not add useful information, it should not have Alt Text read aloud. When the image has already been described as part of the text above, the image can be marked as decorative as well. This keeps the focus on the important content.
For detailed examples across different content types such as graphs, maps, tables, math equations and more refer to the
When describing medical images, clarity and precision are essential. Alt Text should help visually impaired users understand the image’s clinical relevance without compromising patient privacy.
Key Guidelines:
Examples:
For a CT Scan:
“CT scan of the chest showing a large mass in the left lung.”
For an MRI scan:
“MRI of the brain, axial view, showing a hyperintense lesion in the left temporal lobe, suggestive of a glioma.”
For a medical image like an X-ray of a leg:
“X-ray of the right leg, frontal view, showing a transverse fracture of the mid-shaft of the tibia with slight displacement but no visible involvement of the fibula.”&Բ;
The following examples show how to write effective Alt Text for different types of images, based on their purpose and content.
Informative photos should have Alt Text. It is not necessary to describe every detail but highlight the most essential elements relevant to the story.
Provide as much information as possible about the content of infographics, charts, and maps. Do not just state what the graphic is about; describe the key aspects of the information within it. If you cannot describe everything, prioritize the most valuable information. Use surrounding text and captions for additional details.
In the case of images of mathematical expressions, the Alt Text should describe the expression in spoken mathematics. Avoid using symbols or characters with mathematical usages (such as operators, fractions, units etc.) which may not be announced as expected by screen readers.
If you have a simple headshot where the caption includes the person's name and the photo does not add any additional information, Alt Text is not needed. The caption already provides the necessary details.
For decorative images like stock photos or illustrations that do not add meaningful content to the story, you usually do not need captions or Alt Text. However, if the image supports a concept in the story or is the main image, adding Alt Text can enhance the user's experience.
The alt-text should be the name of the organization/website. It is not necessary to add words as “logo”. It is also not necessary to say “link to…” because screen readers already announce to users that they are on a link.
