gistfile1.php

<?php

$width = 400;
$height = 300;

$canvas = imagecreatetruecolor($width, $height);

imagefilledrectangle($canvas, 0, 0, $width, $height, imagecolorallocatealpha($canvas, 0, 0, 0, 0));

imagefilledarc($canvas, 200, 150, $width / 2, $height / 2, 45, 135, imagecolorallocatealpha($canvas, 255, 255, 255, 0), IMG_ARC_CHORD /* | IMG_ARC_NOFILL */);

imagejpeg($canvas, '/path/to/chord.jpg');