title: Fatal error: Call to undefined function imagefilter()
body: <p>What is causing this error?</p>
  
  <pre>
  Fatal error: Call to undefined function imagefilter() in /var/www/polaroid.php on line 5
  </pre>
  
  <pre><code>  1 &lt;?PHP
    2   $img_addr = $_GET['image_address'];
    3   $img = imagecreatefromjpeg($img_addr);
    4
        /* everything works as expected without this line */
    5   imagefilter($img, IMG_FILTER_GRAYSCALE);  
    6
    7   if ($img)
    8   {
          /* I moved the header function here so I can see errors in the browser. 
             If I leave it at the top of the file, the browser expects an image 
             and doesn't print the error messages. */
    9     header('Content-type: image/jpeg');
   10     imagejpeg($img);
   11   }
   12 ?&gt;
   13
  </code></pre>
  
  <p>This is the URL I use:</p>
  
  <pre>
  http://localhost/polaroid.php?image_address=http://mattnelsoninfo.files.wordpress.com/2008/04/ceiling_cat1.jpg
  </pre>
  
  <p>NOTE: gd is listed in the output from phpinfo(). </p>
  
  <h2>EDIT: I'm using PHP Version 5.2.6-2ubuntu4.1</h2>
  
  <h2>Another EDIT:</h2>
  
  <p>phpinfo() yields this in the gd section</p>
  
  <pre><code>gd
  GD Support  enabled
  GD Version  2.0 or higher
  FreeType Support    enabled
  FreeType Linkage    with freetype
  FreeType Version    2.3.7
  T1Lib Support   enabled
  GIF Read Support    enabled
  GIF Create Support  enabled
  JPG Support     enabled
  PNG Support     enabled
  WBMP Support    enabled 
  </code></pre>
  
  <p>Thanks!</p>