How can I align text to an image automatically in PHP?

I have a few lines of code to generate a plain image with some given text in php. But when I give width for image text goes outside the image. How can I align text inside the image with a fixed width but dynamic height? My code is given below.

header ("Content-type: image/png");
$string = 'Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industrys standard dummy text ever since the 1500s';                                            
$font   = 4;
$width  = ImageFontWidth($font) * strlen($string);
$height = ImageFontHeight($font);

$im = @imagecreate (200,500);
$background_color = imagecolorallocate ($im, 255, 255, 255); //white background
$text_color = imagecolorallocate ($im, 0, 0,0);//black text
imagestring ($im, $font, 0, 0,  $string, $text_color);
imagepng ($im);

I want this image to automatically adjust texts based on given paragraph. How to do that?

You may try this : (based on gannon's contribution at http://php.net/manual/en/function.imagestring.php)

header ("Content-type: image/png");
$string = "Lorem Ipsum is simply dummy\n text of the printing and typesetting industry. Lorem Ipsum has been the industrys standard dummy text ever since the 1500s";
$im = make_wrapped_txt($string, 0, 4, 4, 200);
imagepng ($im);

function make_wrapped_txt($txt, $color=000000, $space=4, $font=4, $w=300) {
  if (strlen($color) != 6) $color = 000000;
  $int = hexdec($color);
  $h = imagefontheight($font);
  $fw = imagefontwidth($font);
  $txt = explode("\n", wordwrap($txt, ($w / $fw), "\n"));
  $lines = count($txt);
  $im = imagecreate($w, (($h * $lines) + ($lines * $space)));
  $bg = imagecolorallocate($im, 255, 255, 255);
  $color = imagecolorallocate($im, 0xFF & ($int >> 0x10), 0xFF & ($int >> 0x8), 0xFF & $int);
  $y = 0;
  foreach ($txt as $text) {
    $x = (($w - ($fw * strlen($text))) / 2); 
    imagestring($im, $font, $x, $y, $text, $color);
    $y += ($h + $space);
  }
  return $im;
}

Giving this kind of result :