The alt attribute provides a textual alternative to an image.
It is used whenever the actual image cannot be rendered.
Common reasons for that include:
Empty alt attributes are not allowed, since purely decorative images should be specified using CSS, not using the img
tag.
<img src="foo.png" /> <!-- Noncompliant --> <img src="foo.png" alt="" /> <!-- Noncompliant --> <input type="image" src="bar.png" /> <!-- Noncompliant -->
<img src="foo.png" alt="Some textual description of foo.png" /> <input type="image" src="bar.png" alt="Textual description of bar.png" />