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      The author probably forgot to link to the NNGroup source study that they referred to in the article:

      1. Alt text: not always needed
      2. Alt Text: What to Write

      Over all, they explain whether or not to include an alt description; and what to write in the alt description. The second article provides a nice decision tree.

      I’ve so far used a similar but simpler approach, described in this stackoverflow answer:

      1. For a majority of illustrative images, where associated description could benefit sighted users too, put the image inside a figure, and describe it with a figcaption. The alt attribute becomes redundant in that case. The posted article and its source study describes well what to put in the figcaption as description.

      2. Functional images, or actionable images, like one used as a link or a button, should be given an alt attribute. The description should pretty much describe the action.