When to Add Empty alt Attribute to HTML img Element?

The empty alt attribute (i.e. alt="") indicates that the image is not an important part of the content. Adding an empty alt attribute is typically done when:

• The image does not convey any meaning (e.g. image is transparent);
• The image does not add anything useful to the document (e.g. image is used as a decoration or a tracking pixel).

For example:

<img src="tracking-pixel.gif" alt="" />

In such cases, the user agent may choose to omit/ignore the image, for example, when:

• The image appears broken (because the resource might be unreachable for example);
• The image is unsupported or invalid;
• The image is being interpreted by non-visual browsers (such as screen readers, text-only browsers, etc.) or assistive technologies (such as braille readers, etc.);
• Images are turned off by the user in a visual browser (for example, to save bandwidth or mobile data, for privacy reasons, etc.).

When this happens, the user agent may provide the user with a notification (or some sort of indication) that an image is present but has been omitted from rendering.