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。
二、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。
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。
程序运行效果如下图所示：
三、实现方法：
ClickCaptcha.class.php类文件如下：
<?php /** Click Captcha 验证码类 * Date: 2013-05-04 * Author: fdipzone * Ver: 1.0 */ class ClickCaptcha { // class start public $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示例程序如下：
<?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="https://www.jb51.net/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="https://www.jb51.net/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 method="post" action="https://www.jb51.net/demo.php" onsubmit="return false"> <p>name:<input type="text"></p> <p>Captcha:Please click full circle<br><img src="demo.php?get_captcha=1&t=<?=time() ?>"></p> <p><input type="submit" value="submit"></p> <input type="hidden" value="true"> <input type="hidden"> </form> </body> </html> <?php } ?>