All images require alt text.
Images can be integral or important to the text, or just decorative. If the image is important to the text, the alt text should provide a full description of it and what it shows:
Murrumbidgee River at Wagga Wagga showing the erosion of the bank caused by the combination of recent dry periods and stock incursions
However, if the description is lengthy and already included elsewhere in the document, the alt text can simply note this location (see Dealing with lengthy alt text):
Murrumbidgee River at Wagga Wagga (long description is in the caption text)
If the image is only decorative, set the alt text as follows:
- in HTML, set as ALT=” “ (no space between quote marks)
- in Microsoft Word, set as Decorative
- In Adobe Acrobat, set as Background.
If the image is a photograph or illustration, it is not usually necessary to include phrases such as photograph of or image of in the alt text – this is inferred from the tag on the image that a screen reader will recognise. However, if the fact that the image is a photograph (rather than a painting or a cartoon) is important, include this in the alt text.
If the image is a diagram, include the type of diagram (eg Venn diagram, process map) in the alt text:
Venn diagram showing 2 intersecting circles. One circle is labelled Owls. The other circle is labelled Crows.
• Circle 1, Owls: eat mice and rats, have a hooked beak, use other birds’ nests.
• Circle 2, Crows: eat seeds and insects, build nests.
• Area of intersection: lay eggs, care for young.
It is important to add alt text for images because software programs may generate their own automatic alt text using image recognition. This automatic alt text may not have accurately recognised the image and may produce incorrect text.
For more information, see Writing alternative (alt) text.
