总是提示验证码不正确，请问如何

//form提交页面index.jsp
<%@page language="java" contentType="text/html;charset=gb2312"%>
<html>
<head>
<title>
后台管理系统---新东方电脑教育集团
</title>
<script language="JavaScript">function check(check_login_info){
  if (check_login_info.usr_id.value==""){
  alert ("请输入【管理员帐号】");
  check_login_info.usr_id.focus();
  return false;
  }
    if (check_login_info.usr_pwd.value==""){
  alert ("请输入【管理员密码】");
  check_login_info.usr_pwd.focus();
  return false;
  }  
  return true;
}
</script>
<link href="../include/css/button.css" rel="stylesheet" type="text/css">
<link href="../include/css/kingv.css" rel="stylesheet" type="text/css">
<link href="../include/css/sroll.css" rel="stylesheet" type="text/css">
<link href="../include/css/style.css" rel="stylesheet" type="text/css">
<link href="../include/css/system.css" rel="stylesheet" type="text/css">
</head>
<body background="images/win_bg.jpg" leftmargin="0" topmargin="0" >
<table width="100%" height="100%" border="0">
  <tr>
    <td align="center" valign="middle"><div align="center">
        <table width="693" height="457" border="0" align="center">
          <tr>
            <td height="453" background="images/main_bg.jpg"><table width="693" height="326" border="0">
                <tr> 
                  <td colspan="3">&nbsp;</td>
                </tr>
                <tr> 
                  <td height="29" colspan="3">&nbsp;</td>
                </tr>
                <tr> 
                  <td height="24">&nbsp;</td>
                  <td width="382" height="24">&nbsp;</td>
                  <td height="24">&nbsp;</td>
                </tr>
                <tr> 
                  <td width="156">&nbsp;</td>
                  <td><form action="Check_Login.jsp" method="post" name="check_login_info" onSubmit="return check(this)">
                      <table width="100%" border="0" class="bodystyle">
                        <tr> 
                          <td colspan="3">&nbsp;</td>
                        </tr>
                        <tr> 
                          <td class="wahfengmid"><div align="right"></div></td>
                          <td>&nbsp;</td>
                          <td>&nbsp;</td>
                        </tr>
                        <tr> 
                          <td class="wahfengmid"><div align="right"></div></td>
                          <td>&nbsp;</td>
                          <td>&nbsp;</td>
                        </tr>
                        <tr> 
                          <td class="wahfengmid"><div align="right"></div></td>
                          <td>&nbsp;</td>
                          <td>&nbsp;</td>
                        </tr>
                        <tr>
                          <td class="wahfengmid"><div align="right"></div></td>
                          <td>&nbsp;</td>
                          <td>&nbsp;</td>
                        </tr>
                        <tr> 
                          <td width="35%" class="wahfengmid"><div align="right"></div></td>
                          <td width="58%">&nbsp;</td>
                          <td width="7%">&nbsp;</td>
                        </tr>
                        <tr> 
                          <td class="wahfengmid"><div align="right" class="wahfengmid">管理帐号：</div></td>
                          <td>
<input name="usr_id" type="text" id="usr_id"  style="background-image: url('images/pwd_bg.jpg'); color: #FF0000" size="24"></td>
                          <td>&nbsp;</td>
                        </tr>
                        <tr> 
                          <td><div align="right"></div></td>
                          <td>&nbsp;</td>
                          <td>&nbsp;</td>
                        </tr>
                        <tr> 
                          <td><div align="right" class="wahfengmid">管理密码：</div></td>
                          <td>
<input name="usr_pwd" type="password" id="usr_pwd" style="background-image: url('images/pwd_bg.jpg'); color: #FF0000" size="24"></td>
                          <td>&nbsp;</td>
                        </tr>
                        <tr>
                          <td>&nbsp;</td>
                          <td>&nbsp;</td>
                          <td>&nbsp;</td>
                        </tr>
                        <tr> 
                          <td><div align="right"><span class="wahfengmid">验 证 码：</span></div></td>
                          <td>
                            <div align="left"> 
                              <input name="my_check_t" type="text" id="my_check_t"  style="background-image: url('images/pwd_bg.jpg'); color: #FF0000" size="10" maxlength="8">
                              <span class="unnamed1">
                             <%
int number=(int)(Math.random()*1000000)+1;
out.print(number);%>
 
                              <input name="my_check_h" type="hidden" id="my_check_h" value="<%=number%>">
                              </span>                            </div></td>
                          <td>&nbsp;</td>
                        </tr>
                        <tr> 
                          <td colspan="3">&nbsp;</td>
                        </tr>
                        <tr> 
                          <td colspan="3"><div align="center" class="wahfengmid"> 
                              <p> 
                                <input type="submit" name="Submit" value="点击进入管理系统" style="background-image: url('images/Button_bg.jpg'); font-weight: bold">
                              </p>
                            </div></td>
                        </tr>
                      </table>
                    </form></td>
                  <td width="141">&nbsp;</td>
                </tr>
              </table></td>
          </tr>
        </table>
      </div></td>
  </tr>
</table>
</body>
</html>
//Check_Login.jsp
<%@ page contentType="text/html;charset=gb2312"%>
<%@ page import="java.sql.*"%>
<html>
<%
//java.lang.String checkt;
String checkt,checkh;
checkt=request.getParameter("my_check_t");
//java.lang.String checkh;
checkh=request.getParameter("my_check_h");
if(checkt!=checkh);
{
    out.print("<script>window.alert('验证码不正确');window.location.href='index.jsp'</script>");
}
%>
<body>
<%//链接数据库
String user="sa";
String password="";
Class.forName("com.microsoft.jdbc.sqlserver.SQLServerDriver").newInstance();
String url="jdbc:microsoft:sqlserver://localhost:1433;DatabaseName=kingvsql";
Connection conn= DriverManager.getConnection(url,user,password);
//转换上页传递过来的值，原为字符型，现转换为整型
String User,Pwd;
User=request.getParameter("usr_id");
Pwd=request.getParameter("usr_pwd");
Statement stmt=conn.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,ResultSet.CONCUR_UPDATABLE);
String sql="select * from Kingv_Login where Kingv_Login_Username='"+User+"' and Kingv_Login_Password='"+Pwd+"'";
ResultSet rs=stmt.executeQuery(sql);
%><table border="1"><tr bgcolor="#cccccc">
<td width="59">
序号</td>
<td width="54"> 帐号</td>
<td width="75">密码</td>
<td width="57">链接</td>
<td width="143">&nbsp;</td>
<tr><%while (rs.next()){%>
<tr>
<td>&nbsp;
</td>
<td>
<%=rs.getString(2)%></td>
<td>
<%=rs.getString(3)%></td>
<td><a href="Data_Show.jsp">恭喜，登录成功</a></td>
<td>&nbsp;</td>
<tr>
<%}%></table><%rs.close();
stmt.close();
conn.close();
%>
</body>
</html>