Cannot modify header information - headers already sent in...

ob_start();
$img_r = imagecreatefromjpeg($src);
$dst_r = ImageCreateTrueColor($targ_w, $targ_h);	
imagecopyresampled($dst_r, $img_r, 0, 0, $x, $y, $targ_w, $targ_h, $w, $h);
flush();
ob_flush();
header('Content-type: image/jpeg');
imagejpeg($dst_r, null, $jpeg_quality);
ImageJPEG($dst_r, $src_new);	
ImageDestroy($img_r);
ImageDestroy($dst_r);