需求：
现在常用的表单验证码大部分都是要用户输入为主，但这样对手机用户会不方便。
如果手机用户访问，可以不用输入，而是click某一位置便可确认验证码，这样就会方便很多。
原理：
1.使用PHP imagecreate创建PNG图象，在图中画N个圆弧，其中一个是完整的圆(验证用)，将圆心坐标及半径记录入session。
2.在浏览器，当用户在验证码图片上点击时，记录点击的位置。
3.将用户点击的坐标与session记录的圆心坐标、半径比较，判断是否在圆中，如是则验证通过。
ClickCaptcha.class.php
<?php
/** Click Captcha 验证码类
* Date: 2013-05-04
* Author: fdipzone
* Ver: 1.0
*/class ClickCaptcha { // class startpublic $sess_name = 'm_captcha';public $width = 500;public $height = 200;public $icon = 5;public $iconColor = array(255, 255, 0);public $backgroundColor = array(0, 0, 0);public $iconSize = 56;private $_img_res = null;public function __construct($sess_name=''){if(session_id() == ''){session_start();}if($sess_name!=''){$this->sess_name = $sess_name; // 设置session name}}/** 创建验证码 */public function create(){// 创建图象$this->_img_res = imagecreate($this->width, $this->height);// 填充背景ImageColorAllocate($this->_img_res, $this->backgroundColor[0], $this->backgroundColor[1], $this->backgroundColor[2]);// 分配颜色$col_ellipse = imagecolorallocate($this->_img_res, $this->iconColor[0], $this->iconColor[1], $this->iconColor[2]);$minArea = $this->iconSize/2+3;// 混淆用图象,不完整的圆for($i=0; $i<$this->icon; $i++){$x = mt_rand($minArea, $this->width-$minArea);$y = mt_rand($minArea, $this->height-$minArea);$s = mt_rand(0, 360);$e = $s + 330;imagearc($this->_img_res, $x, $y, $this->iconSize, $this->iconSize, $s, $e, $col_ellipse); }// 验证用图象,完整的圆$x = mt_rand($minArea, $this->width-$minArea);$y = mt_rand($minArea, $this->height-$minArea);$r = $this->iconSize/2;imagearc($this->_img_res, $x, $y, $this->iconSize, $this->iconSize, 0, 360, $col_ellipse); // 记录圆心坐标及半径$this->captcha_session($this->sess_name, array($x, $y, $r));// 生成图象Header("Content-type: image/PNG");ImagePNG($this->_img_res);ImageDestroy($this->_img_res);exit();}/** 检查验证码* @param String $captcha 验证码* @param int $flag 验证成功后 0:不清除session 1:清除session* @return boolean*/public function check($captcha, $flag=1){if(trim($captcha)==''){return false;}if(!is_array($this->captcha_session($this->sess_name))){return false;}list($px, $py) = explode(',', $captcha);list($cx, $cy, $cr) = $this->captcha_session($this->sess_name);if(isset($px) && is_numeric($px) && isset($py) && is_numeric($py) && isset($cx) && is_numeric($cx) && isset($cy) && is_numeric($cy) && isset($cr) && is_numeric($cr)){if($this->pointInArea($px,$py,$cx,$cy,$cr)){if($flag==1){$this->captcha_session($this->sess_name,'');}return true;}}return false;}/** 判断点是否在圆中* @param int $px 点x* @param int $py 点y* @param int $cx 圆心x* @param int $cy 圆心y* @param int $cr 圆半径* sqrt(x^2+y^2)<r*/private function pointInArea($px, $py, $cx, $cy, $cr){$x = $cx-$px;$y = $cy-$py;return round(sqrt($x*$x + $y*$y))<$cr;}/** 验证码session处理方法* @param String $name captcha session name* @param String $value* @return String*/private function captcha_session($name,$value=null){if(isset($value)){if($value!==''){$_SESSION[$name] = $value;}else{unset($_SESSION[$name]);}}else{return isset($_SESSION[$name])? $_SESSION[$name] : '';}}} // class end?>demo.php
<?php
session_start();
require('ClickCaptcha.class.php');if(isset($_GET['get_captcha'])){ // get captcha$obj = new ClickCaptcha();$obj->create();exit();
}if(isset($_POST['send']) && $_POST['send']=='true'){ // submit$name = isset($_POST['name'])? trim($_POST['name']) : '';$captcha = isset($_POST['captcha'])? trim($_POST['captcha']) : '';$obj = new ClickCaptcha();if($obj->check($captcha)){echo 'your name is:'.$name;}else{echo 'captcha not match';}echo ' <a href="demo.php">back</a>';}else{ // html
?>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"><title> Click Captcha Demo </title><script type="text/javascript" src="jquery-1.6.2.min.js"></script><script type="text/javascript">$(function(){$('#captcha_img').click(function(e){var x = e.pageX - $(this).offset().left;var y = e.pageY - $(this).offset().top;$('#captcha').val(x+','+y);})$('#btn').click(function(e){if($.trim($('#name').val())==''){alert('Please input name!');return false;}if($.trim($('#captcha').val())==''){alert('Please click captcha!');return false;}$('#form1')[0].submit();})})</script></head><body><form name="form1" id="form1" method="post" action="demo.php" οnsubmit="return false"><p>name:<input type="text" name="name" id="name"></p><p>Captcha:Please click full circle<br><img id="captcha_img" src="demo.php?get_captcha=1&t=<?=time() ?>" style="cursor:pointer"></p><p><input type="submit" id="btn" value="submit"></p><input type="hidden" name="send" value="true"><input type="hidden" name="captcha" id="captcha"></form></body>
</html>
<?php } ?>源码下载：点击下载
