Image_Graphviz Example shows nothing

i´m trying to use Image_开发者_C百科Graphviz from pear. I installed the package via pear install. All went fine, pear list displays the package as stable. When I try to display the given example there´s just an empty page. Do I need to install more than the pear package? I tryed with PHP 5.3.2 and PHP 5.2.7

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As the manual page states:

Calling graphviz' dot or neato is being done by Image_GraphViz implicitly when calling image() or fetch().

So you need to install the graphviz program on your machine, and have it available in your path.