Alt text, or alt tag, is a term used to describe text that is read by a screen reader in place of an image. When a screen reader encounters an image, for example, it will skip over it unless there is alt text provided to read in its place.
Alt text usually identifies the type of image (photo vs. graph, for instance) and spells out any relevant details needed for someone who is visually impaired to understand the material. There are two types of alt text to provide: short and long.
- Short alt text is roughly a single sentence and provides a broad description of the image. In some cases, this may be the only alt text needed. For example, a simple photograph may require a single sentence of explanation.
- Long alt text can be multiple sentences or paragraphs, depending on the complexity of the image and the type of information that needs to be provided. For example, a graph would always include long alt text, as students will need to hear details about trends and/or specific data points.