Alternate, or alt, text appears on the image placeholder while the image is downloading from the web; it also substitutes for graphics that fail to download. In some newer versions of browsers, the text also appears next to the pointer as a tooltip.

Entering brief, meaningful alternate text has become increasingly important in web design. A growing number of visually impaired people are using screen-reading applications, which read alternate text in a computer-generated voice as the pointer passes over graphics on a web page.

To specify alt text for a selected slice or hotspot: