<%@ import namespace="System"%>
<%@ import namespace="System.io"%>
<%@ import namespace="System.Drawing"%>
<%@ import namespace="System.Drawing.Imaging"%>
<script language="vb" runat="server">
Sub Page_Load(Sender as object,e as eventargs)
'RndNum是一个
自定义函数
dim VNum as string=RndNum(4)
Session("VNum")=VNum
ValidateCode(VNum)
End Sub
'生成图象验证码函数
Sub ValidateCode(VNum)
Dim Img as System.Drawing.Bitmap
Dim g as Graphics
Dim ms as MemoryStream
dim gheight as integer=Int(Len(VNum)*11.5)
'gheight为图片宽度,根据字符长度自动更改图片宽度
img=new BitMap(Gheight,20)
g=Graphics.FromImage(img)
g.DrawString(VNum,(New Font("Arial",10)),(New SolidBrush(color.blue)),3,3)'在矩形内绘制字串（字串，字体，画笔颜色，左上x.左上y）
ms=New MemoryStream()
img.Save(ms,ImageFormat.Png)
Response.ClearContent() '需要输出图象信息 要修改HTTP头
Response.ContentType="image/Png"
Response.BinaryWrite(ms.ToArray())
g.Dispose()
img.Dispose()
Response.End()
End Sub
'--------------------------------------------
'函数名称:RndNum
'函数参数:VcodeNum--设定返回
随机字符串的位数
'函数功能:产生数字和字符混合的随机字符串
Function RndNum(VcodeNum)
dim Vchar as string="0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,W,X,Y,Z"
dim VcArray() as string=split(Vchar,",") '将字符串生成数组
dim VNum as string=""
dim i as byte
For i=1 to VcodeNum
Randomize
VNum=VNum & VcArray(Int(35*Rnd)) '数组一般从0开始读取，所以这里为35*Rnd
Next
Return VNum
End Function
</script>
二，详细代码如下，保存为ValidateCode.aspx，并把它和gif.aspx放在同一目录下，在浏览器中打开ValidateCode.aspx，即可测试效果：
<script language="vb" Runat="Server">
Sub Page_Load(Sender as object,e as eventargs)
dim VNum as string=Session("VNum")
Session.Abandon()
ViewState("VNum")=VNum
End Sub
'以下事件代码是用来测试验证码,可以根据需要更改
Sub btnSubmit_click(sender as object,e as eventargs)
'判断输入的验证码与所给是否相同
If txtValidateCode.text=Cstr(ViewState("VNum")) then
lblShow.text="<font color='red'>提示:验证通过</font>"
Else
lblShow.text="所填写的验证码与所给的不符"
End If
End Sub
</script>
<html>
<body>
<form runat="server">
<div align="center">
<table width="750">
<!--DWLayoutTable-->
<tr>
<td width="256" height="46"> </td>
<td width="9"> </td>
<td width="88"> </td>
<td width="87"> </td>
<td width="100"> </td>
<td width="68"> </td>
<td width="97"> </td>
</tr>
<tr>
<td height="21"></td>
<td></td>
<td colspan="3" valign="top"><asp:label ID="lblShow" runat="server"></asp:label></td>
<td> </td>
<td> </td>
</tr>
<tr>
<td height="14"></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
<tr>
<td height="21"> </td>
<td colspan="2" valign="middle">验证码:</td>
<td valign="top"><asp:Image id="Image1" runat="server" ImageUrl="gif.aspx" /></td>
<td> </td>
<td> </td>
<td> </td>
</tr>
<tr>
<td height="20"> </td>
<td colspan="2" valign="top">输入验证码:</td>
<td valign="top"><asp:textbox ID="txtValidateCode" runat="server" TextMode="SingleLine" /></td>
<td colspan="2" valign="middle"><font color="#FF0000" size="2">*注意:区分大小写</font></td>
<td> </td>
</tr>
<tr>
<td height="25"> </td>
<td> </td>
<td> </td>
<td> </td>
<td> </td>
<td> </td>
<td> </td>
</tr>
<tr>
<td height="19"> </td>
<td> </td>
<td> </td>
<td valign="top"><asp:button ID="btnSubmit" runat="server" Text="比较" onclick="btnSubmit_click" /></td>
<td> </td>
<td> </td>
<td> </td>
</tr>
</table>
</div>
</form>
</body>
</html>
