Web Accessibility eClass

Lecture on Images Part 3: How to Write Short Text Alternatives

To ascertain appropriate alt text think about why an image is being included in a document. Every image has a reason for being on a page because it either is purely decorative or provides information. By first establishing image purpose your decision of how to write appropriate text alternatives for different types of images becomes easier. So first decide if the image is 1.) merely eye candy i.e. bullets, spacers, or box corners or 2.) if it contributes to understanding, functionality, and/or appreciation of page content. Then go from there.

Example Markup

The following are six common types of images and example short text alternative markup:

1. Purely Decorative Images
2. Pictures
3. Images of Text
4. Complex Data Images
5. Symbols
6. Functional Images

General alt Text Good Practices

• Be succinct as possible while still conveying equivalent values. Short text that describes an image's purpose or gives an overview will often suffice. While there is no official length restriction on the length of alt text, many experts recommend 125 characters or fewer because of restrictions within some user agents.
• Provide the same informational content as the image.
• For a purely decorative (eye candy) image, which provides absolutely no content or functional information use a null alt attribute: alt="".
• Avoid redundant alt text. An example of this would be repeating the same text in your document, as well as in the alt attribute, and is unnecessary.
• Whenever an image is not decorative, concisely explain or label what the image is in the context of the document's purpose without overly duplicating the text in which the image is embedded.
• Where an image performs a specific function, such as a graphical link, provide information about its functionality or a name that identifies the content of the destination.
• Write suitable alt text according to context. The same image in a different situation may need very different alt text.

Context Affects Short Text Alternatives

What's necessary and what's not depends a lot on the function of the image and its context on the page. The same image may require alt text in one spot, but not in another. In the following video Derek Featherstone discusses how context impacts writing appropriate alt text. A transcript of Accessibility: Images in Context is also available.

WebAIM provides further examples in Context is Everything.

alt Terminology

The term "alt tag" is sometimes incorrectly used instead of the correct term "alt attribute". Actually as hard core developers will tell you, in HTML their is no such thing as an "alt tag". Technically, tags are things like <p> or </p> that you use to mark up your page and the alt attribute sits inside a tag, like this: <img alt="">, but sometimes you'll hear people refer to this attribute as an "alt tag" so it's good to be aware of this terminology even though it is incorrect. Calling an attribute a tag is a common mistake. An attribute is a property of an element that is written within the start-tag of an element, and should be referred to as simply an attribute. The text within the quotation marks is called "alt text".

What's Next?

Once you've finished part 3 of the lecture, please continue reading part 4.