Alt text guidelines

Do:

• Aim for about 120 characters of text or 1-2 sentences
• Be specific & accurate with your alt-text
• Be objective & neutral in your descriptions
• Consider your intended audience and what they need to understand about the image
• Be careful when marking images as decorative

Avoid:

• Starting your alt-text with “Image of” (Caveat: It’s ok to indicate what kind of image has been included, including “Screenshot of”, “Black and white image of”, “graphic of”, or “cartoon”; most screen readers say “Image:” leading into the alt-text, so starting with “Image” causes the word to be repeated)
• Including every detail in the image
• Confusing images captions with alt-text
• Blindly using AI generated alt-text

Alt-text v captions

Alt-text:

• Describes what the user needs from the image
• Usually not visible on the page

Captions:

• Identify what the image is about: citation information
• Snippets of context
• Can be read on the page

(based on TTaDA’s “Simple Images”)

Markdown

• Pandoc’s markdown includes alt text automatically
• R Markdown knitr code chunks need to have fig.alt="alt text" (note that lm.plot creates separate figures, so fig.alt should be a character vector of the appropriate length)