登录的验证码设计

 <%
 dim rndnum,verifycode
 Randomize
 Do While Len(rndnum)<4
 num1=CStr(Chr((57-48)*rnd+48))
 rndnum=rndnum&num1
 loop
 session("verifycode")=rndnum
%>

<% 
 '首先判断输入的验证码是否正确
 dim verifycode1,verifycode2
 verifycode1=trim(Request.Form("verifycode1"))
 verifycode2=trim(Request.Form("verifycode2"))
 if verifycode1<>verifycode2 then
 response.write"<SCRIPT language=JavaScript>alert('您输入的验证码不正确。');"
 response.write"location.href='index.asp'</SCRIPT>"
 else
 session("verifycode")=""
%>

<tr>
            <td align="center" height=30>验证码：<input name="verifycode1" id="verifycode1" style="border-style:solid;border-width:1;padding-left:4;padding-right:4;padding-top:1;padding-bottom:1" onFocus="this.select(); " onmouseover="this.style.background='#EAEAEA';" onmouseout="this.style.background='#FFFFFF'" size="12" maxlength="4">
                          <font color="#000000" size="2"><%=session("verifycode")%>
                                <input type="hidden" name="verifycode2" value="<%=session("verifycode")%>"></td>
          </tr>