Custom Captcha

<a href="#" onclick="document.getElementById('img_captcha').src = 'captcha/script.php?a='+Math.round(Math.random()*10000);"><img src="captcha/script.php" id="img_captcha" border="0" /></a>

<?php
session_start();
// characters to use when generating random string
$chr = 'abcdefghkmnpqrstuvwxyz0123456789';
// array of fonts to use (in same directory)
$ttf = array(
    'arial.ttf',
    'barrettprime.ttf',
    'gabriola.ttf'
);
// random sizes to use in pt
$siz = array(
    20,
    25,
    30,
    35
);
// random colors to use per character
$txtC = array(
    '000000',
    '333333',
    '990000',
    '009900'
);
// random colors to use per background (soon will be replaced with images)
$bd = array(
    'CCCCCC',
    '999999'
);
// mininum amount of random characters generated
$min = 4;
// maximum amount of random characters generated
$max = 8;
/* NO NEED TO EDIT BELOW */
$ltp = 2;
$len = rand($min, $max);

function hex2rgb($c){
    if(!$c) return false;
    $c = trim($c);
    $out = false;
    $c = str_replace('#','', $c);
    $l = strlen($c) == 3 ? 1 : (strlen($c) == 6 ? 2 : false);
    
    if($l){
        unset($out);
        $out[0] = hexdec(substr($c, 0,1*$l));
        $out[1] = hexdec(substr($c, 1*$l,1*$l));
        $out[2] = hexdec(substr($c, 2*$l,1*$l));
    }else
        $out = false;
          
    return $out;
}
function genRand($char, $length){
    $rtn = '';
    for($i=0;$i<$length;$i++){
        $rtn .= $char{rand(0, strlen($char)-1)};
    }
    return($rtn);
}
$spc = 40;
$wid = $len * $spc;
$hei = 50;
$cpt = genRand($chr, $len);
$_SESSION['captcha_key'] = md5($cpt);
$captcha = imagecreate($wid, $hei);
$bgR = hex2rgb($bd[rand(0, count($bd)-1)]);
$bg = imagecolorallocate($captcha, $bgR[0], $bgR[1], $bgR[2]);

imagerectangle($captcha, 0, 0, $wid, $hei, $bg);

// DRAW captcha
$ang = 20;

for($i=0;$i<strlen($cpt);$i++){
    $c = $cpt[$i];
    $a = rand(-1*$ang, $ang);
    $bgR = hex2rgb($txtC[rand(0, count($txtC)-1)]);
    $fg = imagecolorallocate($captcha, $bgR[0], $bgR[1], $bgR[2]);
    $ch = rand(0, count($ttf)-1);
    $si = $siz[$ch];
    $ft = $ttf[$ch];
    $bx = imagettfbbox($si, $a, $ft, $c);
    $ii = $i; $ii++;
    $ww = $bx[2] - $bx[0]; if($ww<0) $ww*=-1;
    $hh = $bx[3] - $bx[5]; if($hh<0) $hh*=-1;
    $add =  rand($i*$spc, $i*$spc+($spc-$ww));
    $rnX = $i*$spc + rand($ltp, $spc-$ww-$ltp);
    $rnY = $hh + rand($ltp, $hei-$hh-$ltp);
    $xb = imagettftext($captcha, $si, $a, $rnX, $rnY, $fg, $ft, $c);
}
// next fn
function wave_area($img, $x, $y, $width, $height, $amplitude = 10, $period = 10){
    // Make a copy of the image twice the size
    $height2 = $height * 2;
    $width2 = $width * 2;
    $img2 = imagecreatetruecolor($width2, $height2);
    imagecopyresampled($img2, $img, 0, 0, $x, $y, $width2, $height2, $width, $height);
    if($period == 0) $period = 1;
    // Wave it
    for($i = 0; $i < ($width2); $i += 2)
        imagecopy($img2, $img2, $x + $i - 2, $y + sin($i / $period) * $amplitude, $x + $i, $y, 2, $height2);
    // Resample it down again
    imagecopyresampled($img, $img2, $x, $y, 0, 0, $width, $height, $width2, $height2);
    imagedestroy($img2);
}
wave_area($captcha, 0, 0, $wid, $hei, 3, 6);

header("Content-type: image/png");
imagepng($captcha);
?>