What is Alternative Text?
Images convey information quickly and powerfully—assuming they can been seen and understood. However, some readers may not understand the meaning of the image; others may not be able to see it due to visual impairment, personal viewing preferences (especially on the web), or technological limitations.
Alternate text (often called “alt text” or "alt tag") is added to an image to provide a textual alternative to visual information. Why is this important? Remember, some users won’t see your information; instead, they’ll hear it using screen-reading software. By adding an alt text to an image, you make its meaning available to people who, for whatever reason, cannot see it.
The following video clips demonstrate what images sound like to someone using a screen reader. The first is an example of an accessible image with alt text. The second shows what happens when alt text is not included.