Displaying an image created with imagecreatefromstring

Let's say I have the code that looks something like:

<?PHP

//
//... stuff here
//

$im = imagecreatefromstring( $imageData );

echo "<img src=" . /* what goes here? */ . "alt=\"the image\" />";


//
// more stuff here
//
?>

What do I replace /* what goes here? */ with so my image data will display?

Thank you.