title: How to use ImageMagick to substract a image from another?
body: <p>I have this two images :</p>
  <p><a href="https://i.stack.imgur.com/yyMgK.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/yyMgK.jpg" alt="First" /></a><br />
  <sub>(source: <a href="http://hubscher.remy.free.fr/tally/images/2011/01/24/first591.jpg" rel="nofollow noreferrer">free.fr</a>)</sub></p>
  <p><a href="https://i.stack.imgur.com/cq0rM.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/cq0rM.jpg" alt="Second" /></a><br />
  <sub>(source: <a href="http://hubscher.remy.free.fr/tally/images/2011/01/24/second593.jpg" rel="nofollow noreferrer">free.fr</a>)</sub></p>
  <p>How can I use imagemagick to remove the background (second picture) from the first one ?</p>
  <p>Cheers,</p>
  <p>Rémy</p>
  <p>Here I made you a final but simple example :</p>
  <p><a href="http://noosphere.ionyse.com/transparent_example/transparent_difference.png" rel="nofollow noreferrer">Transparent Overlay http://noosphere.ionyse.com/transparent_example/transparent_difference.png</a>
  <a href="http://noosphere.ionyse.com/transparent_example/background.png" rel="nofollow noreferrer">Background http://noosphere.ionyse.com/transparent_example/background.png</a></p>
  <p><a href="http://noosphere.ionyse.com/transparent_example/background-example.png" rel="nofollow noreferrer">Example 1 http://noosphere.ionyse.com/transparent_example/background-example.png</a>
  <a href="http://noosphere.ionyse.com/transparent_example/background-example2.png" rel="nofollow noreferrer">Example 2 http://noosphere.ionyse.com/transparent_example/background-example2.png</a></p>
  <p>Here you see that anywhere I put the transparent overlay on the background I get the perfect match using the opacity of the overlay PNG.</p>
  <p>I would like to be able to calculate this overlay image. Do you think it is possible using ImageMagick ?</p>