It is right there in the spec:

    <dt>A start tag whose tag name is "image"</dt>
    <dd>
     <!-- As of 2005-12, studies showed that around 0.2% of pages used the <image> element. -->
     <p><a href="#parse-error">Parse error</a>. Change the token's tag name to "img" and reprocess it. (Don't
    ask.)</p>
   </dd>