CSS background images cannot and should not have alternate text
I sometimes see people asking how they can provide alternate text for CSS background images. The answer is that you can’t. Neither should you need to.
The reason, as Chris Heilmann explains in So how do you add alternative text to background images?, is that a background image should be used for presentational purposes only, i.e. it should not be essential for understanding the content or functionality of the page.
If you turn off CSS in your web browser and find that vital information disappears because background images are no longer visible, it is a clear indication that those images should be
img elements with proper alternate text.
This post is a Quick Tip. Background info is available in Quick Tips for web developers and web designers.