captcha

<?php
session_start();
$nbr_chiffres = 4;
header ("Content-type: image/png");
$_img = imagecreatefrompng('images/fond_verif_img.png');
$arriere_plan = imagecolorallocate($_img, 0, 0, 0);
$param1 = rand(0,255);
$param2 = rand(0,255);
$param3 = rand(0,255);
$avant_plan = imagecolorallocate($_img, $param1, $param2, $param3);
$i = 0;
while($i < $nbr_chiffres)
{
        $chiffre = mt_rand(0, 9);
        $chiffres[$i] = $chiffre;
        $i++;
}
$nombre = null;
foreach ($chiffres as $caractere)
{
        $nombre .= $caractere;
}
$_SESSION['aleat_nbr'] = $nombre;
unset($chiffre);
unset($i);
unset($caractere);
unset($chiffres);
imagestring($_img, 5, 7, 2, $nombre, $avant_plan);
imagepng($_img);
?>