error en captcha

[roboty]

hola intento crear un captcha pero ma da error pongo codigo por si me podeis ayudar?

Código PHP:

<?php
date_default_timezone_set('Europe/Madrid');
session_start();
$captchaTextSize = 7;
do {
    $md5Hash = md5( microtime( ) * date() );
    preg_replace( '([1aeilou0])', "", $md5Hash );
}
while( strlen( $md5Hash ) < $captchaTextSize );
    $key = substr( $md5Hash, 0, $captchaTextSize );
    $_SESSION['key'] = md5( $key );
    $captchaImage = imagecreatefrompng( "imagenes/captcha.png" );
    $textColor = imagecolorallocate( $captchaImage, 50, 105, 82 );
    $lineColor = imagecolorallocate( $captchaImage, 15, 103, 103 );
    $imageInfo = getimagesize( "imagenes/captcha.png" );
    $linesToDraw = 10;
    for( $i = 0; $i < $linesToDraw; $i++ )  {
        $xStart = mt_rand( 0, $imageInfo[ 0 ] );
        $xEnd = mt_rand( 0, $imageInfo[ 0 ] );
        imageline( $captchaImage, $xStart, 0, $xEnd, $imageInfo[1], $lineColor );
    }
    imagettftext( $captchaImage, 20, 0, 35, 35, $textColor, "fuente/VeraBd.ttf", $key );
    header ( "Content-type: image/png" );
    imagepng( $captchaImage );
?>