captcha.php

<?php 
    $letters = 'ABCDEFGKIJKLMNOPQRSTUVWXYZ';

    $caplen = 6;
    $width = 120; $height = 40;
    $font = 'fonts/comic.ttf';
    $fontsize = 14;

    header('Content-type: image/png');

    $im = imagecreatetruecolor($width, $height); 
    imagesavealpha($im, true); 

    $bg = imagecolorallocatealpha($im, 0, 0, 0, 127);
    imagefill($im, 0, 0, $bg);

    putenv( 'GDFONTPATH=' . realpath('.') ); 

    $captcha = '';
    for ($i = 0; $i < $caplen; $i++){
        $captcha .= $letters[ rand(0, strlen($letters)-1) ]; 
        $x = ($width - 20) / $caplen * $i + 10;
        $x = rand($x, $x+4);
        $y = $height - ( ($height - $fontsize) / 2 );
        $curcolor = imagecolorallocate( $im, rand(0, 100), rand(0, 100), rand(0, 100) );
        $angle = rand(-25, 25);
        imagettftext($im, $fontsize, $angle, $x, $y, $curcolor, $font, $captcha[$i]); 
    }


    session_start();

    $_SESSION['capcha'] = $captcha;

    imagepng($im); 
    imagedestroy($im);
?>