displaying BLOB data from DB

[eluser]junaids[/eluser]
here my controller

Code:

function image()
          {
             $u = $this->session->userdata('username');
             $this->db->where('username', $u);
            $image_data = $this->images->get($Profile_picture);
            $image = imagecreatefromstring($image_data);
              header('Content-Type: image/png');
            imagepng($image);
            imagedestroy($image);
            exit;
          }

and here the view where i m displaying the image.
<img >

no image is displayed. any idea?