<?php
  namespace Admin\Controller;
  use Think\Controller;
  use Think\Verify;
  class LoginController extends Controller{
    public function login(){
      if($_POST){
        $obj = new Verify();
        if($obj->check(I('post.yanzhengma','','trim'))){
          // 注释部分为另外一种从数据库中验证密码的方法
          // $data['name'] = I('post.user_name');
          // $data['psd'] = I('post.password');
          // $row = M('user')->where($data)->find();
          $name = I('post.user_name');
          $psd = I('post.password');
          $str = 'name ="'.$name. '" and tel = "'.$psd.'"';
          var_dump($str);
          $row = M('user')->where($str)->find();
          if($row)
            $this->redirect("Index/index");
          else
            $this->redirect('login','',1,'用户名或密码错误');
        }
        else{
          $this->redirect('login','',1,'验证码错误');
        }
      }
      $this->display();
    }
    public function verifyImg(){
      //设置验证码的宽高字体大小以及验证码的个数，设计其他的参照Think\Verify里面的设置
      $config=array(
        'imageW'  => 150,
        'imageH'  => 40,
        'fontSize' => 20,
        'length'  => 4
      );
      $obj = new \Think\Verify($config);
      $obj->entry();
    }
  }

<form action="login" method="post">
  <table valign="top" width="50%">
 <tr><td colspan="2"><h4 style="letter-spacing:1px;font-size:16px;">RainMan 网站管理后台</h4></td></tr>
 <tr><td>管理员：</td><td><input type="text" name="user_name" value="" /></td></tr>
 <tr><td>密    码：</td><td><input type="password" name="password" value="" /></td></tr>
 <tr><td>验证码：</td>
   <td><input type="text" name="yanzhengma" value="" style="width:80px;"/></td>
   <td><img src="__URL__/verifyImg" onclick="this.src='__URL__/verifyImg/'+Math.random()" alt=""/></td>
 </tr>
 <tr class="bt" align="center"><td> <input type="submit" value="登陆" /></td><td> <input type="reset" value="重填" /></td></tr>
  </table>
</form>