title: I get this "Error while running convert: sh: convert: command not found"
body: <p>I'm trying to use the gem called <code>Simple Captcha</code></p>
  
  <p>This requires ImageMagick installed on the machine.
  I've installed it and <code>convert --version</code> shows this</p>
  
  <pre><code>Version: ImageMagick 6.8.2-10 2013-02-12 Q16 http://www.imagemagick.org
  Copyright: Copyright (C) 1999-2013 ImageMagick Studio LLC
  Features: DPC OpenMP
  Delegates: bzlib freetype jng jpeg lcms png ps tiff x xml zlib
  </code></pre>
  
  <p>However, it won't show the generated image when SimpleCaptcha is working.<br>
  So I took a look at the log. and it says this</p>
  
  <pre><code>  StandardError (Error while running convert: sh: convert: command not found):
    galetahub-simple_captcha (0.1.3) lib/simple_captcha/utils.rb:17:in `run'
    galetahub-simple_captcha (0.1.3) lib/simple_captcha/image.rb:76:in `generate_simple_captcha_image'
    galetahub-simple_captcha (0.1.3) lib/simple_captcha/middleware.rb:36:in `make_image'
    galetahub-simple_captcha (0.1.3) lib/simple_captcha/middleware.rb:18:in `call'
    ...
  </code></pre>
  
  <p>How can I solve this?</p>