What Is Alt Text?
Alt text (short for "alternative text") is the text that a screen reader will read out loud when an image, graphic or table is encountered on the page.
example of an alt text description as read by a screen reader.
Alt text might also be referred to as an "alt tag," "alt attribute" or image description.
Figure 1, screenshot of an image and alt text field in Word.
Note: Depending on the tool/software you are using, you may be presented with a field for "title" and/or "description" for entering alt text. Regardless of the tool/software, always use the description field for entering alt text.
Why Add Alt Text?
Alt text allows screen readers to read information about images out loud to users who are blind or and visually impaired. Alternative text is necessary so that people who are blind or visually impaired can still access the information provided by an image and understand the purpose of the image.
On a website like dcccd.edu or like eCampus, the alt text also appears in place of the image if it fails to load due to a slow connection speed or other issues.
General Guidelines for Alt Text
- Be precise. The alt text should describe the content in the image accurately.
- Limit the alt text to relevant information. You don't need to describe every single detail, just those that matter in terms of how the image is being used in context and what information the reader needs to retain. For example, alt text might describe what a person would need to remember for a test or understand an image used in an email.
- Imagine you closed your eyes and you couldn't see the image. What description is necessary for the reader to understand the information presented in the image?
- Keep it concise. A short phrase or sentence will be enough for many images.
- Avoid using "image of" at the beginning of the description. It's not necessary since the screen reader will already announce that it is an image.
- If an image is simply decorative, then the alternative text can just be the word "null" or "decorative."
- If you have infographics or images of text (like charts and tables), the alt text should state all of the information provided, including every word that appears on the image. Alternatively, you can provide a text version of the information.
- There are times when alternative text can't equate to the purpose of the image. Consider what process you would follow in the classroom or in your office to accommodate a person who is blind. This same process will suffice for the web.
- Captions may also work in place of lengthy alt text if the content is explained elsewhere in the document. Example: "Figure 1, this infographic shows pie charts of the information explained below."