php实现字母数字混合验证码

Vendor('Vcode.Vcode', '', '.class.php'); 
$config = array("width" => 100, "height" => 36, "count" => 4, "str" => 2); //配置 
$vcode = new Vcode($config); 
$vcode->getCode(); //获取验证码 
$vcode->getImg(); //输出图片 
exit;

<img src="__APP__/code/" id="code" onclick="changeCode($('#code'))"/>

function changeCode(obj) { 
 obj.attr("src", '__APP__/code/?' + Math.random()); 
}

<input type="text" id="input_code" class="input"/> 
<input type="button" value="提交" class="btn" onclick="checkCode()"/>
function checkCode() { 
  $.post("__APP__/Code/check", {code: $("#input_code").val()}, function(data) { 
    if (data == '1') { 
      alert("验证码正确！"); 
    } else { 
      alert("验证码错误！"); 
    } 
  }, "json") 
}

public function check() { 
    $code = I('post.code'); 
    if (strtolower($code) == $_SESSION["sucaihuo_code"]) { 
      echo "1"; 
    } else { 
      echo "-1"; 
    } 
}