In order to make sure that the GD installed the following example would be run. The example creates a very simple image using just pure GD calls and outputs an image in PNG format. This could be considered a smoke-test to see that the GD library is available from PHP. Please note that this is an absolute pre-requisite in order for the JpGraph library to work at all.
Store the code snippet below somewhere in the document root and make sure it runs correctly.
  $im = @
ImageCreate (
150, 100)
    or die (
"Cannot create a new GD image.");
$background_color 
= ImageColorAllocate 
($im, 255, 
255, 255);
$text_color 
= ImageColorAllocate 
($im, 233, 
14, 91);
ImageString 
($im, 1, 
5, 5,  "A Simple Text String", $text_color
);
header ("Content-type: image/png");
ImagePng ($im);
If the above script does not work or some error or warnings are printed on the screen then it is necessary to correct those problems before proceeding with the installation.