用asp编写验证码

<div align="center"><font size="2">校验码
<%
for i=1 to 4
Randomize
rnum=int(rnd()*35)+1
str="0123456789abcdefghijkLmnopqrstuvwxyz"
selectstr=selectstr&mid(str,rnum,1)
next
for i=1 to 4
imgname=mid(selectstr,i,1)
%><img src="../images/picpwd/<%=imgname%>.gif" width="22" height="15"><%
next
%>
<input type=hidden name="picpwd" value="<%=selectstr%>">
</font></div>