Ensuring sufficient contrast between background colors and images is necessary to ensure that users who have difficulty distinguishing contrasts are able to read your publication. Avoid overlaying text on noisy (multi-color) background images, and relying on positioning to avoid color contrasts, as different reading system may reflow content in unexpected ways.
Also ensure that background images do not convey information necessary to understand the publication, or to be able to interact with it. Unlike embedded images, backgrounds cannot be given text alternatives or descriptions and a user will not know a change has occurred.
background-image property remains largely unsupported because of the reflowable
nature of EPUBs. Although support may increase as fixed-layout publications get supported, use of
images is not recommended in general, reflowable publications.
For fixed layout publications, try to limit backgrounds to simple atmospheres. If components of the
background are important to comprehension, see if they can be overlaid using
img tags so
that descriptions can be added.