将PHP生成的文本指向Google免费Web字体

Can some one let me know how I can use google web fonts for creating text captcha?

<?php
  $img          = imagecreatetruecolor(200, 200);
  $bgColor      = imagecolorallocate($img, 255, 255, 255);
  $netColor     = imagecolorallocate($img, 185, 185, 185);
  $txtColor     = imagecolorallocate($img, 0, 0, 0);
  imagefill($img, 0, 0, $bgColor);
  imagettftext($img, 22, 0, 50 ,45, $txtColor,"Bedizen.ttf","Expert" ); 
  header("Content-type:image/png");
  imagepng($img);
  imagedestroy($img);
?>

As you can see from above code I am using a font file to render the text but is there any way to navigate to one of Google free web fonts? Thanks

For anyone that stumbles across this question (as I did) - this is do-able. As Marc commented, you need to download the font from Google Fonts, upload to your webserver and include it that way.

I needed to include the full path to the font eg:

imagettftext($img, 22, 0, 50 ,45, $txtColor,"/path/to/webroot/fonts/Downlo-Bold.ttf","Expert" );