Any image that has a "usemap" attribute must have links replicated somewhere else in the document.

Example

Wrong

<p><map name="imagemap" id="map1"><area shape="poly" coords="185,0,355,0,295,123" href="horses.html" alt="horses"/><area shape="poly" coords="336,202,549,203,549" href="dogs.html" alt="dogs"/><area shape="rect" coords="0,10,172,10" href="birds.html" alt="birds"/></map></p><p><img src="navigation.gif" usemap="#imagemap" alt="navigation"/></p>

Right

<map name="imagemap" id="map1"><area shape="poly" coords="185,0,355,0,295,123" href="horses.html" alt="horses"/><area shape="poly" coords="336,202,549,203,549" href="dogs.html" alt="dogs"/><area shape="rect" coords="0,10,172,10" href="birds.html" alt="birds"/></map></p><p><img src="navigation.gif" usemap="#imagemap" alt="navigation"/></p><p><a href="horses.html">Horses</a> | <a href="dogs.html">Dogs</a> | <a href="birds.html">Birds</a></p>