====== ImageMagick ======
A trier :
  * http://www.imagemagick.org/script/mogrify.php
  * http://www.imagemagick.org/script/escape.php
  * http://www.imagemagick.org/Usage/resize/
  * https://www.linuxquestions.org/questions/linux-general-1/getting-image-size-imagemagick-352671/
  * http://www.fmwconcepts.com/imagemagick/index.php
  * http://blog.dorian-depriester.fr/linux/creer-et-editer-des-gif-animes-avec-imagemagick