Writing effective alternative text for images
The function of alternative text (alt text) is to provide a description alternative to non-text content in web pages. Alternative text serves many purposes, but as computers and screen readers are unable to analyse an image, the main function of alt text is to describe what is being presented. Alt text enables the content and function of the image to be accessible to those with visual or cognitive disabilities.
It’s about the context
When deciding upon appropriate alternative text, context is key. The alt text should differ based on the context of the image. When writing effective alt text there are several main principles that you should follow:
- Be as specific as possible
- Keep it short and succinct; the most popular screen readers will automatically cut off alt text at approximately 125 characters
- Use keywords
- Don’t forget form buttons; image buttons should have an alternative attribute that describes the function of the button.
Alternative text for images
Spacer images, which are invisible images used to create space on the page, should be given null alternative text or alt=”.
Bullets and icons should be treated in the same way as spacer images and given a null alt text or alt=”. This is because if the alt text “Bullet” is assigned to each image then the screen reader would read aloud “Image, bullet” before each item, resulting in a longer time to work through the list.
Decorative images should also be given a null alternative text or alt=” as they have no benefit to the end user.
Websites will vary how they apply alt text for logos; some may say ‘company name’ and some may say ‘company name logo’ and others may describe the function of the image, for instance taking you back to the homepage and so say ‘back to homepage’.
Within navigation menus the alternative text shouldn’t be used to expand on the image; if the menu item says ‘Information’ then the alt text should also say ‘Information’. Alt text should repeat the text word for word. If you wish to expand on the navigation you should use the title attribute.
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