Accessibility: Visual guidelines - Colour, text and layout
Provide alternative text for images
It is extremely important that you provide alt attributes for all images and other visual elements. Failure to fill these in is usually one of the single most common causes of WAI Priority 1 failure. Alt tags are important for users who have visual impairments or for users who have chosen to turn off images in their browsers.
An alt attribute should be as descriptive as possible – if in doubt, imagine how the image would be described to someone over the telephone.
An alt attribute for the image on this page might read 'Photograph of an old milestone partly obscured by bracken so that the place name cannot be seen'.
Think about how you might describe this photograph to someone who could not see.
Blur effects on images
Avoid using blur effects on images to mark something in an interface as being unimportant or inactive. If these are used people with low vision or using magnifiers may not realise that the graphic is not intended to be read.
Graphics used for text elements
Do not create graphics for text elements - use CSS stylesheets to control presentation of text.
Embedding text inside a graphic file is a bad idea because this immediately introduces an accessibility problem. The user will not be able to resize or change the colour scheme of content inside a graphic. The look and feel of text on the web should be controlled by the use of stylesheets.