Draw string on png image in PHP

<?php//from   ww w  .j  a  v a  2  s . c o  m
    define("WIDTH", 300);
    define("HEIGHT", 100);

    $img = imagecreate(WIDTH, HEIGHT);

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

    imagerectangle($img, 0, 0, WIDTH-1, HEIGHT-1, $black);

    $start_x = 10;
    $start_y = 10;

    for($font_num = 1; $font_num <= 5; $font_num++) {
        imagestring($img, $font_num, $start_x,$start_y, "Font #$font_num", $black);
        $start_y += 15;
    }

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