Code:
<?php
error_reporting(0);
session_start();

$txt = $_SESSION['CaptchaWord'];
if (!isset($txt)) { $txt = $_GET['CaptchaWord']; } //test
if (!isset($txt)) { $txt = 'test'; }
$txt = trim($txt);
$colorR = $_SESSION['colorR'];
if ($colorR == -1) { $colorR = rand(50,200); } // -1 je default vr.
$colorG = $_SESSION['colorG'];
if ($colorG == -1) { $colorG = rand(50,200); } // -1 je default vr.
$colorB = $_SESSION['colorB'];
if ($colorB == -1) { $colorB = rand(50,200); } // -1 je default vr.

$myTextLen = strlen($txt);

$safeemail = imagecreate($myTextLen*15,40);
$backcolor = imagecolorallocate($safeemail,255,255,255);
$textcolor = imagecolorallocate($safeemail,$colorR,$colorG,$colorB);
$textcolor2 = imagecolorallocate($safeemail,$colorB,$colorR,$colorG);
$textcolor3 = imagecolorallocate($safeemail,$colorG,$colorG,$colorG);
imagefill($safeemail,0,0,$backcolor);
imagestring($safeemail,12,0,10,$txt,$textcolor);
imagestring($safeemail,20,10,0,$txt,$textcolor2);
imagestring($safeemail,20,rand(0,$myTextLen*15-10),rand(0,30),$txt,$textcolor3);
imagecolortransparent($safeemail,$backcolor);
header("Content-type: image/gif");
imagegif($safeemail);
imagedestroy($safeemail);
?>