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:

• The image can no longer be found
• Slow internet connections, while waiting for the image to download
• Visually impaired users using a screen reader software
• Images loading is disabled, e.g. to reduce data consumption on mobile phones

The following code illustrates this rule:

<img src="foo.png" />                                           <!-- Non-Compliant -->
<input type="image" src="foo.png" />                            <!-- Non-Compliant -->
<img src="foo.png" alt="Some textual description of foo.png" /> <!-- Compliant -->
<input type="image" src="foo.png" alt="..." />                  <!-- Compliant -->