动态生成验证码图片

using System;
using System.IO;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Drawing.Imaging;
using System.Web;
using System.Web.SessionState;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;

namespace Vildate
{
/// <summary>
/// YZgif 的摘要说明。
/// </summary>
public class YZgif : System.Web.UI.Page
{
private void Page_Load(object sender, System.EventArgs e)
{
string VNum = "";
VNum = this.RndNum(4);
Session["VNum"] = VNum;
this.ValidataCode(VNum);
}

#region Web Form Designer generated code
override protected void OnInit(EventArgs e)
{
//
// CODEGEN：该调用是 ASP.NET Web 窗体设计器所必需的。
//
InitializeComponent();
base.OnInit(e);
}

/// <summary>
/// 设计器支持所需的方法 - 不要使用代码编辑器修改
/// 此方法的内容。
/// </summary>
private void InitializeComponent()
{
this.Load += new System.EventHandler(this.Page_Load);
}
#endregion

public void ValidataCode(string str)
{
System.Drawing.Bitmap Img;
Graphics g;
MemoryStream ms;
int gheight = str.Length*11;
Img = new Bitmap(gheight,20);
g = Graphics.FromImage(Img);
SolidBrush sb = new SolidBrush(Color.DarkSlateBlue);
Font ft = new Font("Arial",10);
g.DrawString(str,ft,sb,3,3);
ms = new MemoryStream();
Img.Save(ms,ImageFormat.Png);
Response.ClearContent();
Response.ContentType = "image/Png";
Response.BinaryWrite(ms.ToArray());
g.Dispose();
Img.Dispose();
Response.End();
}
public string RndNum(int i)
{
string VNum = "";
Random Rnd = new Random();
string Vchar = "0,1,2,3,4,5,6,7,8,9,a,s,d,f,g,h,j,k,l,q,w,e,r,t,y,u,i,o,p,z,x,c,v,b,n,m,Q,W,E,R,T,Y,U,I,O,P,A,S,D,F,G,H,J,K,L,Z,X,C,V,B,N,M";
string[] Vc = Vchar.Split(',');
for(int k =0;k<i;k++)
{
VNum = VNum + Vc[Rnd.Next(0,61)];
}
return VNum;
}
}
}

再在需要用验证码的页面加入一个protected System.Web.UI.WebControls.Image Image1;
输入框：protected System.Web.UI.WebControls.TextBox txtyz;
<TD height="35">验证码：</TD> <TD><asp:TextBox id="txtyz" runat="server" BorderColor="#333333" BorderWidth="1px" BorderStyle="Solid" Width="180px"></asp:TextBox></TD> <TD><asp:Image id="Image1" runat="server" ImageUrl="YZgif.aspx"></asp:Image></TD>

if(this.txtyz.Text == Session["VNum"].ToString())
{}
else
{}