title: Zend captcha Image generates blank
body: <p>The image captcha randomly displays a blank captch. Roughly 4 out of 10 attempts. </p>
  
  <p>I have already discovered the problem and <a href="http://forums.zend.com/viewtopic.php?f=69&amp;t=5812" rel="nofollow">a post on the zend forum suggest</a> the only fix is to edit the Zend Framework code. </p>
  
  <p>Is there any way to fix this without editing the ZF code?
  How come Zend have not fixed this in the releases since then, I have a look in the change log but nothing related to this?</p>
  
  <pre><code>$w     = $this-&gt;getWidth();
  $h     = $this-&gt;getHeight();
  $fsize = $this-&gt;getFontSize();
  
  $img_file   = $this-&gt;getImgDir() . $id . $this-&gt;getSuffix();
  if(empty($this-&gt;_startImage)) {
      $img = imagecreatetruecolor($w, $h);
  } else {
      $img = imagecreatefrompng($this-&gt;_startImage);
      if(!$img) {
          require_once 'Zend/Captcha/Exception.php';
          throw new Zend_Captcha_Exception("Can not load start image");
      }
      $w = imagesx($img);
      $h = imagesy($img);
  }
  $text_color = imagecolorallocate($img, 0, 0, 0);
  $bg_color   = imagecolorallocate($img, 255, 255, 255);
  imagefilledrectangle($img, 0, 0, $w-1, $h-1, $bg_color);
  $textbox = imageftbbox($fsize, 0, $font, $word);
  $x = ($w - ($textbox[2] - $textbox[0])) / 2;
  $y = ($h - ($textbox[7] - $textbox[1])) / 2;
  
  // Edit: check not over 100
  if($x &gt; 50){ $x = 50;}
  if($y &gt; 100){ $y = 100;}
  
  imagefttext($img, $fsize, 0, $x, $y, $text_color, $font, $word);
  </code></pre>
  
  <p><strong>Debugging with a die() proves this is the case:</strong></p>
  
  <pre><code>die("img=".$img ." fsize=".$fsize. " x=".$x ." y=".$y . " h=".$h );
  img=Resource id #159 fsize=24 x=1073741923.5 y=41 h=50
  </code></pre>