Images can be useful to illustrate a point, but they should not be used as a replacement for a clear text description.
Images must be no more than 600 pixels wide but can be longer than 600 pixels. Always consider usability when determining the length of an image; it needs to be fully visible on-screen without too much scrolling.
Do not use text in images. If it cannot be avoided, the same text must be explained as a long description nearby on the page or in the alt text. This is so that it can be changed into other forms such as braille, speech or symbols.
Avoid using colour alone to convey meaning in an image, as users with visual disabilities can find it hard to distinguish between them. Using red and green together is a common example as many people are unable to tell these colours apart. If you have to use colour to help explain something – check it with colour blindness software.
Maps with multiple clickable areas should provide an explanation in the alt text or in the text nearby that gives an overall context to the meaning of the map.