Step 3: Write an Appropriate Description

The bulk of your alt text will be the description of the image. With your purpose in mind, you will want to start filling in details.

For an image, such as a photograph or cartoon that is serving an aesthetic—rather than educational—purpose, the description will likely be very short and simple, only a sentence long. Is it a photo of a child playing? A dog? That simple identification—presented as short alt text—may be enough.

For a figure, such as a graph or chart, that is being used to illustrate a concept or depict a specific type of graph or chart, you will want to ignore the actual data and text. Consider instead what features a student will need to know to visualize it. Does it include a title? A key? Arrows? Descriptive text and labels? Plotted points?

For a figure, such as a graph or chart, that is depicting specific data or concepts, you will want to consider the level of detail necessary to provide a fair reading experience. In these cases, you will likely be providing long alt text as well. For example:

  • One important thing to consider with flow charts is if the elements of the chart are discrete or the concept being depicted is broken into ordered steps or stages.
  • For a graph that is depicting specific data, remember that you likely can’t describe every data point in your alt text unless it’s a very simple graph. Start by simply describing the overall trends. Is the graphed variable rising, falling, or steady? Will it help students to know of specific variances? Is the text focusing on just a specific part or section of the graph (for instance, a graph of data over years may only need a description of a certain span of time based on the context and what you would like students to focus on)? Is it relevant for students to know the highest and/or lowest points?
  • For a photograph that is serving a content-related purpose, you will want to consider the degree of detail necessary to relay the information. After identifying the main subject of the photo, home in on the details needed. Consider what the surrounding text or caption is describing. Is the background of the photo important, or just the subject? Is the composition important? Is there an action that needs to be identified? Do not include details that are irrelevant for students to know, but do include the details they will need to better understand the concepts.

Another thing to consider when writing the description of any image serving an educational purpose is whether the surrounding text or caption are asking students to analyze, evaluate, or extrapolate specific information from the image. If so, you will want to ensure those data points or elements are provided in your alt text. For example:

  • With a graph, a minimal alt text description of “average height trends upward from age 5 to age 15” will not allow students to the answer the question of the average height at age 7.
  • With a photo, a minimal alt text description of “a person sitting in a chair” will not allow students to the answer the question of how the facial expression invokes open communication.

Overall, the important thing to keep in mind is to exercise restraint and only provide needed information, without providing interpretation. You ideally want the provision of the image and the alt text to be both equitable and equivalent. Keeping this in mind:

  • With a graph, if students really only need a select range of information from the graph, it would be unfair for visually impaired students to need to sort through an endless list of data points, when those who can view the graph could quickly focus in on only the needed section. It would also be unfair for non-visually impaired students to need to perform math calculations based on data, if you provide information not directly given by the graph—such as averages of data points—in the alt text.
  • With a photo, if students really only need to know the basic subject of a photo, it would be unfair for visually impaired students to need to listen to paragraphs of description, when those who can view the photograph could quickly move past it. It would also be unfair for non-visually impaired students to need to provide reasoning for why a photograph depicts a key concept, if you provide information not directly given by the photograph—such as the reason why eye contact is important during a speech—in the alt text.