Using an empty “alt” attribute is allowed only when the Img element needs to be ignored by Assistive Technology. If this image has text or meaning, add content to the alt attribute
Engine scans the page for
<IMG> elements with empty alt attributes
Users who use assistive tools, such as screen readers rely on the alternative text. Images with null alt get ignored by the assistive tools, therefore the users may miss some content.
<img src="/example_"squiggle.gif" width="20" height="20" alt="example_" />