Alternative Text
Alternative text provides a textual alternative to non-text content in web pages, if serves several functions:
- It is read by screen readers in place of images allowing the content and function of the image to be accessible to those with visual or certain cognitive disabilities.
- It is displayed in place of the image in browsers if the image file is not loaded or when the user has chosen not to view images.
- It provides a semantic meaning and description to images which can be read by search engines or be used to later determine the content of the image from page context alone.
Well-formed Alternative Text
Alternative attribute should usually:
- Be accurate and equivalent in presenting the same content and function of the image.
- Be succinct. This means the correct content (if there is content) and function (if there is a function) of the image should be presented as succinctly as is appropriate. Typically no more than a few words are necessary, though rarely a short sentence or two may be appropriate.
- NOT be redundant or provide the same information as text within the context of the image.
- NOT use the phrases "image of ..." or "graphic of ..." to describe the image. It usually apparent to the user that it is an image. And if the image is conveying content, it is typically not necessary that the user know that it is an image that is conveying the content, as opposed to text. Consider the following example:
Using the ALT text of ‘Picture of a students’ will not convey the content/purpose of the image effectively. However if you describe the scene of the students the viewer has a much better idea of the meaning of the image and why it was included.