In the case where you want to store the image on disk and later use it in an img-tag you need to get hold of the image map. For this you will have to use the function Graph::GetHTMLImageMap()
An example of the use of this is shown below. With these lines the image will be written to a file. The script then returns a HTML page which contains the Client side image map and an img-tag which will retrieve the previously stored file.
$graph->Stroke( "/usr/local/httpd/htdocs/img/image001.png" );
echo $graph ->GetHTMLImageMap ("myimagemap001" );
echo "<img src=\"img/image001.png\" ISMAP USEMAP=\"#myimagemap001\" border=0>" ;