<%@ 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))         {             //设置画布             using (System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bitImage))             {                 //随机数字                 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();                 //保存到服务器的sessionid中                 HttpContext.Current.Session["YZM"] = result_string;                 //设置文字                 g.DrawString(num_string01 +"+"+ num_string02+"?", new System.Drawing.Font("宋体", 20), System.Drawing.Brushes.Red, new System.Drawing.PointF(0, 0));                 //保存到输出流中                 bitImage.Save(context.Response.OutputStream, System.Drawing.Imaging.ImageFormat.Jpeg);             }         }     }     public bool IsReusable {         get {             return false;         }     } }

<form id="form1" runat="server">     <div>     <%--单击刷新验证码--%>         <img src="YZM.ashx" alt="请输入验证码" 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>