Imagecreatefromjpeg显示资源错误

I am trying to use imagecreatefromjpeg() function, and create image from url.

I use this test link, with picture for testing, but get this error :

resource(13) of type (gd)

Here is part of code:

$src= $_POST['src'];

                    $targ_w = $targ_h = 160;
                    $jpeg_quality = 90;
                    $img_r = imagecreatefromjpeg($src);
                    $dst_r = ImageCreateTrueColor( $targ_w, $targ_h );


               $test= imagejpeg($dst_r, '/path/to/file, 90);

                      var_dump( $test) ;            

Also, try to download picture,store to folder, and then use function from localdirectory, no success...