Keep it short and sweet.
Ask yourself: What visual elements are essential in order to understand the image?
That’s your alt text.
For text, it should be verbatim if it's short.
If text is long, a short summary with only key info: names, titles, dates, locations, or links
Citizen.Coping
Posting this again because a lot of people said they found it helpful! Guide to ALT text: www.perkins.org/resource/how...
