When you're using content like images, charts, graphs, or thumbnails, these need to have text alternatives. 

For simpler content, like images or thumbnails, you must write a short caption that describes what it is. You must also use the alt text feature of the content management system (CMS) you’re using, This should be a descriptive sentence explaining the information conveyed in the image as the alt text. Alt text is what appears on a page if the content does not load. It is also what screen readers read.

For example, your caption could be ‘Andrew Evans and Will Wynne opening the Smart Building office’. Your alt text could be ‘Andrew Evans and Will Wynne surrounded by Smart colleagues on the ground floor celebrating the opening of the new Smart Building office’.

With content that’s more complicated, like graphs or diagrams, it’s not possible to give the same experience with just a short description. There needs to be more information. 

There must be both a short description and a long description. The aim is to create the same experience with your text as you get from the content.

The long description should be on the same page, and close to the content it is detailing.

For example, a graph showing Smart’s growth could say “This graph shows Smart’s growth”. 

The long description could say ‘This graph shows that since 2019 Smart has grown almost 2,000%, with growth accelerating. In 2019 growth was 200%, 2020 growth was 250% and growth in 2021 was 330%’.

This is an accessibility requirement, meeting Success Criterion 1.1.1 Non-text Content, level A.