title: Imagick. Changing a color to be transparent
body: <p>I would like to change the black border of this image :
  <a href="http://dev.loungeup.net/im/" rel="nofollow">http://dev.loungeup.net/im/</a>
  to transparent with Imagick in PHP.</p>
  
  <p>The result image should have the gray border visible, the image inside the gray border visible, and everything outside the gray border (today in black) should be transparent and let the underlying content (in HTML page for example) visible.</p>
  
  <p>I have been through the documentation several times and tried several solutions but did not figure out how to achieve it.</p>
  
  <p>Any help is appreciated.</p>
  
  <p>Thanks</p>