<%@ WebHandler Language="C#" Class="YZM" %>

using System;
using System.Web;

public class YZM : IHttpHandler, System.Web.SessionState.IRequiresSessionState
{

public void ProcessRequest (HttpContext context) {
context.Response.ContentType = "image/JPEG";
using (System.Drawing.Bitmap bitImage = new System.Drawing.Bitmap(130, 100))
{
//設置畫布
using (System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bitImage))
{

//隨機數字
Random my_random = new Random();
int num_01 = my_random.Next(100);
int num_02 = my_random.Next(100);

int result = num_01 + num_02;
string num_string01 = num_01.ToString();
string num_string02 = num_02.ToString();
string result_string = result.ToString();
//保存到服務器的sessionid中
HttpContext.Current.Session["YZM"] = result_string;
//設置文字
g.DrawString(num_string01 +"+"+ num_string02+"?", new System.Drawing.Font("宋體", 20), System.Drawing.Brushes.Red, new System.Drawing.PointF(0, 0));
//保存到輸出流中
bitImage.Save(context.Response.OutputStream, System.Drawing.Imaging.ImageFormat.Jpeg);
}
}
}

public bool IsReusable {
get {
return false;
}
}

}

<form id="form1" runat="server">
<div>
<%--單擊刷新驗證碼--%>
<img src="YZM.ashx" alt="請輸入驗證碼" onclick="this.src='YZM.ashx?aaa='+new Date()" />
</div>
<asp:TextBox ID="TextBox1" runat="server" text=""></asp:TextBox>
<asp:Button ID="Button1" runat="server" onclick="Button1_Click" Text="Button" />
</form>