The following image has an alt attribute "WebAIM - Web Accessibility in Mind".
The following is the same image as above, but this time without an alt attribute.
The following image has an inappropriate null, or empty alt attribute (alt="").
The following image is a link. It has the alt attribute "WebAIM - Web Accessibility in Mind" and links to the WebAIM homepage.
The following image is a link with a missing alt attribute.
The following image is a link with an inappropriate null, or empty alt attribute (alt="").