/covdet_detectors.jpg"></img>
 <div class="caption">
  <span class="content">
    Different detectors can produce a fairly different set of
    features.
  </span>
 </div>
</div>

<!-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -->
<h1 id="tut.covdet.frames">Understanding feature frames</h1>
<!-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -->

<p>To understand the rest of the tutorial, it is important to
understand the geometric meaning of a feature <em>frame</em>. Feat