asp.net 验证码_无噪点

<img id="imgCode" alt="点击刷新验证码" height="20" src="CodeNubImg.aspx" style="cursor: pointer" width="50" onclick="this.src=this.src+'?'" />if (this.txtCode.Text.ToUpper() == Session["verifycode"].ToString().ToUpper()) { }using System;using System.Data;using System.Configuration;using System.Collections;using System.Web;using System.Web.Security;using System.Web.UI;using System.Web.UI.WebControls;using System.Web.UI.WebControls.WebParts;using System.Web.UI.HtmlControls;using System.Drawing;public partial class Admin_CodeNubImg : System.Web.UI.Page{ protected void Page_Load(object sender, EventArgs e) { string NumStr = null; System.Random Rad = new System.Random(); int RadNum = Rad.Next(9999); if (RadNum.ToString().Length != 4) { for (int i = 1; i <= 4 - RadNum.ToString().Length; i++) { NumStr += "0"; } NumStr += RadNum.ToString(); } else { NumStr = RadNum.ToString(); } string str = NumStr; Session["verifycode"] = NumStr; Bitmap image = new Bitmap(50, 20); Graphics g = Graphics.FromImage(image); g.Clear(Color.White); g.DrawString(str, new Font("宋体", 15, System.Drawing.FontStyle.Bold), new SolidBrush(Color.CadetBlue), 0, 0); image.Save(Response.OutputStream, System.Drawing.Imaging.ImageFormat.Gif); Response.Cache.SetNoStore(); }}