Php Image Edit

[DigitalExpl0it]

Im getting a weird error everytime my php script edits a picture

The image “http://ddrose/imgcreate/go.php” cannot be displayed, because it contains errors.

but if I open the image it edited its fine

here is my code

<?
Header("Content-Type: image/jpeg");
if (!isset($_REQUEST["string"]) || $_REQUEST["string"] <= "") { 
$string = "Hello and Welcome!"; 
} else {
$string = $_REQUEST["string"];
}
$id = ImageCreateFromJpeg("test.jpg");
$black = ImageColorAllocate($id, 0, 0, 0);
ImageString($id, 1, 15, 20, $string, $black);
ImageJpeg($id,"test2.jpg");
ImageDestroy($id);
?>

any ideas?