Circle

<?php
$img = imagecreatetruecolor(50, 50);

$black = imagecolorallocate($img, 0, 0, 0);
$white = imagecolorallocate($img, 255, 255, 255);

imagefill($img, 0, 0, $white);

imagearc($img, 15, 15, 20, 20, 0, 360, $black);

header("Content-Type: image/png");
imagepng($img);
?>