How does PHP output a picture

$t =imagecreatetruecolor (100,100);
$red =imagecolorallocate ($t, 255,0,0);
Imagefill ($t, 0,0, $red);
Header (' content-type:image/png ');
Imagepng ($t);
Imagedestroy ($t);
?>
People say with such a piece of code can output a picture, but I use such code to output the following page, for guidance Ah!!!!

Reply to discussion (solution)

Remove all, do not use include and so on to the above code.

Is there a blank line in the back?

Remove all, do not use include and so on to the above code. It's settled, thanks.

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