title: jquery drag and drop question
body: <p>i want to detect to see if an element was dragged out of container.</p>
  
  <p>for example:</p>
  
  <pre><code>&lt;div id="container"&gt;
      &lt;img src="xxx.png" /&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>if i am drag that img element out of the div. i will remove
  the img element, but i do not know how to detect when the img is out of div.</p>
  
  <p>i am use jquery drag and drop library.</p>