Código PHP:
<?php
require_once ('jpgraph/jpgraph.php');
require_once ('jpgraph/jpgraph_line.php');
$datay1 = array(20,7,16,35);
$datay2 = array(6,20,15,22);
// Setup the graph
$graph = new Graph(350,230);
$graph->SetScale("textlin");
$graph->title->Set('Background Image');
$graph->SetBox(false);
$graph->yaxis->HideZeroLabel();
$graph->yaxis->HideLine(false);
$graph->yaxis->HideTicks(false,false);
$graph->xaxis->SetTickLabels(array('En','Fb','Ma','Ab'));
$graph->ygrid->SetFill(false);
$p1 = new LinePlot($datay1);
$p1->SetColor("#55bbdd");
$p1->mark->SetType(MARK_DIAMOND,'',1.0);
$p1->mark->SetColor('#55bbdd');
$p1->mark->SetFillColor('#55bbdd');
$p1->SetCenter();
$graph->Add($p1);
$p2 = new LinePlot($datay2);
$p2->SetStepStyle();
$p2->SetStyle('dashed');
$p2->SetColor('red');
$p2->mark->SetColor('#aaaaaa');
$p2->mark->SetFillColor('#aaaaaa');
$p2->value->SetMargin(14);
//$p2->SetCenter('false');//que aparezca normal esta
$graph->Add($p2);
// Output line
$graph->Stroke();
?>