My press has asked me to provide alt text for the illustrations in my book. What is alt text and are there any guidelines for creating it?
Alternative text (alt text) is a description of the appearance and function of an illustration. This is mainly used for accessibility purposes, such as for visually impaired people using screen readers, as the alt text will help them understand what the image is and why it is there without having to see it. This is also the text that will be shown if the image fails to load on a digital page, helping to give context without the image being present.
Be specific: The main function of alt text is to enable people who can’t see an image to understand what it is, so be specific about what the image is showing. For sighted persons, a general guide is to think if you closed your eyes and someone read the alt text out to you, could you understand what the image is and why it’s relevant? If you can’t see why it’s important, then it’s worth trying to write the text again.
Consider what’s in the surrounding text: What you want to include in your alt text may depend on what is being said in the surrounding text. For example, if you are talking about a specific point on a graph, you may want to highlight what happens at that point in the alt text, for example ‘A CDC graph showing the admissions of patients with COVID-19, with a dip at Jul 21 and spikes at Jan21, Sept 21, and Jan 22’ (dates shortened to fit recommended character count).
Keep it short: Most screen readers will cut off the alt text after approximately 125 characters, so keep the description short and to the point where possible.
Use keywords: Think about the keywords associated with what you are trying to describe and make sure you include them.
Don’t use ‘Image of’: This is already assumed when reading alt text, as that is the function, and so it’s a waste of characters. You should, however, use more specific descriptors where needed, e.g., ‘a graph of…’.
Below are some examples of bad, okay, and good alt text. Whether the alt text is good or not will depend on what you are trying to highlight and demonstrate with the image, but these examples should give you a general idea of the best practices in action:
Bad alt text: A graph
Okay alt text: A graph of the global child mortality rate since 1950
Good alt text: A graph of the global child mortality rate from 1950 to 2012, showing a downward trajectory
Bad alt text: A pie chart about migration
Okay alt text: A pie chart showing the main reason for migration to the UK in 2007
Good alt text: A pie chart showing reasons for migration to the UK in 2007 with ‘definite job’ and ‘formal study’ as the largest sectors
Bad alt text: An image of some children at school
Okay alt text: A group of children working at school desks
Good alt text: A group of children working together on class work at school desks