source: trunk/web/app/plugins/ptitcaptcha.php

<?php
/**
 * Ptitcaptcha : simple php captcha system
 * 
 * @author Jean-Pierre Morfin
 * @license Creative Commons By
 * @license http://creativecommons.org/licenses/by/2.0/fr/
 */
 
/* Change it to have a specific encoding ! */
define("PTITCAPTCHA_ENTROPY","what-ever-you-want");
 
/* Choose length (max 32) */
define("PTITCAPTCHA_LENGTH",5);
 
$GLOBALS["ptitcaptcha_akey"] = md5(uniqid(rand(), true));
 
/**
 * Helper to generate html form tags
 *
 */
class PtitCaptchaHelper
{
        /**
         * Generate IMG Tag
         *
         * @param string $baseuri : relative or absolute path to folder containing this file on web
         * @return IMG Tag
         */
        function generateImgTags($baseuri)
        {
                return "<a href=\"#\"><img alt=\"???\" title=\"?\"".
                        " src=\"".$baseuri."ptitcaptcha.php?pck=".$GLOBALS['ptitcaptcha_akey']."\"".
                        " id=\"ptitcaptcha\"".
                        " onclick=\"javascript:this.src='".$baseuri."ptitcaptcha.php?pck=".
                        $GLOBALS['ptitcaptcha_akey'].
                        "&amp;z='+Math.random();return false;\" /></a>\n";
        }
 
        /**
         * Generate hidden tag (must be in a form)
         *
         * @return input hidden tag
         */
        function generateHiddenTags()
        {
                return "<input type=\"hidden\" name=\"ptitcaptcha_key\" value=\"".$GLOBALS['ptitcaptcha_akey']."\"/>";
        }
 
        /**
         * Generate input tag (must be in a form)
         *
         * @return input tag
         */
        function generateInputTags()
        {
                return "<input type=\"text\" name=\"ptitcaptcha_entry\" value=\"\"/>";
        }
 
        /**
         * Check if user input is correct
         *
         * @return boolean (true=correct, false=incorrect)
         */
        function checkCaptcha()
        {
                if(     isset($_POST['ptitcaptcha_entry']) && 
                        $_POST['ptitcaptcha_entry'] == PtitCaptchaHelper::_getDisplayText($_POST['ptitcaptcha_key']))
                {
                        return true;
                }
                return false;
        }
 
        /**
         * Internal function
         *
         * @param string $pck
         * @return string
         */
        function _getDisplayText($pck)  // internal function
        {
                $src=md5(PTITCAPTCHA_ENTROPY.$pck);
                $txt="";
                for($i=0;$i<PTITCAPTCHA_LENGTH;$i++)
                        $txt.=substr($src,$i*32/PTITCAPTCHA_LENGTH,1);
                return $txt;
        }
}       
 
 
// If script called directly : generate image
if(basename($_SERVER["SCRIPT_NAME"])=="ptitcaptcha.php" && isset($_GET["pck"]))
{
        $width = PTITCAPTCHA_LENGTH*10+10;
        $height = 30;
 
        $image = imagecreatetruecolor($width, $height);
        $bgCol = imagecolorallocate($image, rand(128,255), rand(128,255), rand(128,255));
        imagefilledrectangle($image,0,0,$width,$height,$bgCol);
 
        $txt = PtitCaptchaHelper::_getDisplayText($_GET["pck"]);
 
        for($c=0;$c<PTITCAPTCHA_LENGTH*2;$c++)
        {
                $bgCol = imagecolorallocate($image, rand(100,255), rand(100,255), rand(100,255));
                $x=rand(0,$width);
                $y=rand(0,$height);
                $w=rand(5,$width/2);
                $h=rand(5,$height/2);
                imagefilledrectangle($image,$x,$y,$x+$w,$y+$h,$bgCol);
                imagecolordeallocate($image,$bgCol);
        }
        for($c=0;$c<PTITCAPTCHA_LENGTH;$c++)
        {
                $txtCol = imagecolorallocate($image, rand(0,128) , rand(0,128), rand(0,128));
                imagestring($image,5,5+10*$c,rand(0,10),substr($txt,$c,1),$txtCol);
                imagecolordeallocate($image,$txtCol);
        }
 
        header("Content-type: image/png");
        imagepng($image);
        imagedestroy($image);
}

?>