$filename = dirname(__FILE__) . '/oldfilename.jpg';

$out_filename = 'newfilename.jpg';

if( ! file_exists($filename)){

　　echo 'Not Found' . $filename;

　　exit;

} else {

　　// We'll be outputting a file

　　header('Accept-Ranges: bytes');

　　header('Accept-Length: ' . filesize($filename));

　　// It will be called

　　header('Content-Transfer-Encoding: binary');

　　header('Content-type: application/octet-stream');

　　header('Content-Disposition: attachment; filename=' . $out_filename);

　　header('Content-Type: application/octet-stream; name=' . $out_filename);

　　// The source is in filename
   if(is_file($filename) && is_readable($filename)){

　　　　$file = fopen($filename, "r");

　　　　echo fread($file, filesize($filename));

　　　　fclose($file);
   }

　　exit;

}