In the realm of web accessibility, ensuring that visual content is understandable to everyone is paramount. Two key tools for achieving this are image alt text and image description text. While often used interchangeably, they serve distinct purposes and web browsers and assistive technologies interpret them differently. Understanding the nuances between alt text or description is crucial for creating incisive and user–friendly websites.
Image alt text: the brief and essential substitute
Image alt text, short for “alternative” text, is a concise textual description of an image embedded directly within the HTML code using the alt attribute. Its primary function is to provide a text equivalent of the image when the image cannot be displayed. This occurs for various reasons, such as slow internet connections, broken image links, or when using a screen reader.
For web browsers, alt text acts as a placeholder. If an image fails to load, the browser displays the alt text, allowing the user to understand its intention. Crucially, screen readers, used by individuals with visual impairments, rely heavily on alt text to describe the image. A well–written alt text provides a brief but informative summary, enabling users to grasp the image’s context and relevance to the surrounding content. For example, the alt text for a picture of a sunset might be “Orange and purple sunset over the ocean.”
In the olden days, when the internet was carved into stone tablets and printed out onto papyrus sheets, alt text was also displayed whenever a user had images turned off in their browser. Now that we’ve stopped measuring internet access speeds in baud rates, this is no longer an issue, and I don’t think browsers provide this facility any more!
Image description text: providing richer context
Image description text, on the other hand, is a more detailed explanation of an image, often provided in a separate location on the webpage. While alt text aims for brevity, image descriptions offer a richer narrative, delving into the visual details and conveying more complex information or emotions present in the image.
Web browsers typically don’t directly render image descriptions in the same way they handle alt text. Instead, descriptions are often placed near the image, perhaps as a caption or within the surrounding paragraph. Assistive technologies, particularly screen readers, can access these longer descriptions through specific mechanisms, such as a designated description link associated with the image or through specific ARIA attributes.
Image descriptions are particularly useful for complex images like charts, infographics, or photographs, where a short alt text wouldn’t suffice to convey the necessary information. For instance, a complex chart’s description might detail the categories, their values, and the trend presented in the data.
The latest specifications for HTML suggest that the longdesc attribute previously used may soon be trashed. The modern WAI–ARIA aria–describedby and aria–details attributes offer alternatives and can be used in a similar way.
Comparing usefulness: context is key
The usefulness of alt text or description hinges on the context and complexity of the image.
- For decorative or purely functional images (like a magnifying glass image for search), concise alt text is usually sufficient. In some cases, a null attribute (
alt="") is appropriate to signal to screen readers that the image doesn’t convey essential information. - For informative images hat are integral to understanding the content, both alt text and a description can be beneficial. The alt text provides a quick summary, while the description offers a deeper dive.
- For complex images containing significant data or visual nuances, a longer image description is often essential. The alt text can provide a brief overview, directing users to the more detailed description.
In essence, alt text provides the essential minimum information, ensuring basic accessibility when the image isn’t visible. Image descriptions offer a more comprehensive understanding, catering to users who require more detail or context. A well–rounded approach often involves using both effectively, with concise alt text and a more detailed description when the image warrants it. By understanding the distinct roles of alt text or description, web developers and content creators can build more accessible and inclusive online experiences.
Further reading
Redcentaur services: accessibility in web design
The compelling case for website accessibility
The benefits of an accessibility strategy
Website accessibility: a simple guide to stop excluding visitors
The indispensable need for image alt text
About the author…
Glenn has been a web developer and graphic designer since the early 1990s. He has followed the development of HTML, JavaScript and CSS from the beginning and has caught on to newer technologies, such as PHP.
Never resting, Glenn tries to keep abreast of new developments in his areas of expertise and is always keen to pass on his knowledge to help the web and graphic design community to improve user experience.
Glenn set up Redcentaur to offer easy access to the internet for small businesses and individuals, without the cloud of mysticism that surrounds internet technology. The stated objective of Redcentaur is to demystify the web for the uninitiated by offering easy-to-use, end-to-end web solutions and hosting at accessible prices.
