If including a graphic or image is essential, it is best to provide a meaningful caption and an alternative text description for any image that conveys important information.
Alternative text is supported in most eBook formats to provide a text description that is not usually displayed on screen, but should be recognised and read by the text-to-speech feature in a reading system.
Not all reading systems detect alternative text, so meaningful captions should also be provided stating what the image is of, or a trend or summary of information if this is not given in the main text, for example "Chart showing gradual rise of sales during 2012".
Note also that it is likely that any text within the image will not be interpreted as text by the reading system, so will not respond to font customisation, be read out by text-to-speech or be included in a search. Therefore any important text from the image also needs to be covered in the caption and alternative text description.
Meaningful captions and alternative text descriptions will assist anyone who cannot see the image or finds it hard to interpret. They will help blind users, and also partially sighted users who may see the image, but not clearly enough to interpret it.
Decorative images
Images which are purely decorative and do not add any information (such as borders and section breaks) can be left without alternative text, and a caption is not necessary. Alternative text and image captions should be as succinct and to the point as possible.
We have extensive guidance on writing effective Alt text. is WebAIM also have some useful infortmation on creating accessible images and W3C on alternatives to auditory and visual content.
Watch our video about using images in eBooks