Impact on users

The following is an overview of common image accessibility errors and the impact on users with a disability.

Images without an ALT attribute

When an image is presented without an ALT attribute it will prevent a person who cannot see a picture from having the text alternative read aloud using synthesized speech.

Images with missing ALT attributes

If an ALT attribute is missing, a screen reader may try to present information that it has pulled from the content on the page. This could include the image file name, dimensions or its location on the page. If the image has no ALT attribute, a blind person can’t access it.

Images with incorrect ALT attributes

  • ALT attributes containing additional or extraneous information will prevent keyboard users from accessing the information.
  • ALT attributes containing the image filename provide no useful information.
  • ALT attributes that do not describe the image or its purpose will provide no useful information.
  • ALT attributes that contain the words ‘image’, ‘photo’ or ‘click here’ provide redundant information.

Images that should have empty ALT attributes

  • An ALT attribute used on transparent images or images that convey no content (e.g. decorative only) will distract people using screen readers or text browsers from the page content – the attribute will be read.
  • An ALT attribute used on spacer images (often used to position content) means people using screen readers may hear the word ‘spacer’ multiple times.
  • An ALT attribute used on a linked image that has a text link next to it (with the same target location) means screen reader will hear the same information twice.

Complex images presented without a long description

People who are blind or vision-impaired will not be able to perceive the information conveyed in the image.

Captions not located near an image

A screen reader will not accurately associate the information with the image.

Colour used to convey information on images

  • People who are blind, colour-blind or low-vision will not be able to perceive the information conveyed by the colour differences.
  • Foreground and background colours that are similar or of low contrast can make text unreadable to some users.

Text presented within an image

Using an image to display text will prevent users from adjusting the text presentation to suit their needs and increase readability e.g. changing the font size, foreground and background colour, font family, line spacing or alignment. NB: Images of text can be used where necessary for instances such as logos and branding.

Images and Search Engine Optimisation

The image ALT attribute should not be used for any other purpose than to convey the information contained in the image or purpose of the image. For example the ALT attribute must not include additional information which is not relevant to the image but has been added purely for Search Engine Optimisation (SEO) reasons.