title: How to create an .IMG image of a disc (sd card) without including free space?
body: <p>In Linux, we can do</p>
  
  <pre><code>dd if=/dev/sdb of=bckup.img
  </code></pre>
  
  <p>but if the disk is of 32GB with only 4GB used, the 32GB image file is waste of space-time. Is there any way or tool to create images with only valid data?</p>