asp.net随机验证码

  常用的生成验证码程序 ，图片效果如下：
    

using System; 
using System.IO; 
using System.Drawing; 
using System.Drawing.Imaging; 
using System.Text; 
using System.Collections; 
using System.Web; 
using System.Web.UI; 
using System.Web.UI.WebControls; 
using System.Web.UI.WebControls.WebParts; 
using System.Web.UI.HtmlControls; 
/**//// <summary> 
///  
/// ** asp.net(C#) 生成验证码 ** 
///  
///  File: GenerateCheckCode.aspx.cs 
///  
///  Author: 周振兴 (Zxjay 飘遥) 
///  
///  E-Mail: tda7264@163.com 
///  
///  Date: 07-04-10 
///  
/// </summary> 
public partial class GenerateCheckCode : System.Web.UI.Page 
...{ 
    protected void Page_Load(object sender, EventArgs e) 
    ...{ 
        string chkCode = string.Empty; 
        //颜色列表，用于验证码、噪线、噪点 
        Color[] color =...{ Color.Black, Color.Red, Color.Blue, Color.Green, Color.Orange, Color.Brown, Color.Brown, Color.DarkBlue }; 
        //字体列表，用于验证码 
        string[] font =...{ "Times New Roman", "MS Mincho", "Book Antiqua", "Gungsuh", "PMingLiU", "Impact" }; 
        //验证码的字符集，去掉了一些容易混淆的字符 
        char[] character =...{ '2', '3', '4', '5', '6', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'J', 'K', 'L', 'M', 'N', 'P', 'R', 'S', 'T', 'W', 'X', 'Y' }; 
        Random rnd = new Random(); 
        //生成验证码字符串 
        for (int i = 0; i < 4; i++) 
        ...{ 
            chkCode += character[rnd.Next(character.Length)]; 
        } 
        Bitmap bmp = new Bitmap(100, 40); 
        Graphics g = Graphics.FromImage(bmp); 
        g.Clear(Color.White); 
        //画噪线 
        for (int i = 0; i < 10; i++) 
        ...{ 
            int x1 = rnd.Next(100); 
            int y1 = rnd.Next(40); 
            int x2 = rnd.Next(100); 
            int y2 = rnd.Next(40); 
            Color clr = color[rnd.Next(color.Length)]; 
            g.DrawLine(new Pen(clr), x1, y1, x2, y2); 
        } 
        //画验证码字符串 
        for (int i = 0; i < chkCode.Length; i++) 
        ...{ 
            string fnt = font[rnd.Next(font.Length)]; 
            Font ft = new Font(fnt, 18); 
            Color clr = color[rnd.Next(color.Length)]; 
            g.DrawString(chkCode[i].ToString(), ft, new SolidBrush(clr), (float)i * 20 + 8, (float)8); 
        } 
        //画噪点 
        for (int i = 0; i < 100; i++) 
        ...{ 
            int x = rnd.Next(bmp.Width); 
            int y = rnd.Next(bmp.Height); 
            Color clr = color[rnd.Next(color.Length)]; 
            bmp.SetPixel(x, y, clr); 
        } 
        //清除该页输出缓存，设置该页无缓存 
        Response.Buffer = true; 
        Response.ExpiresAbsolute = System.DateTime.Now.AddMilliseconds(0); 
        Response.Expires = 0; 
        Response.CacheControl = "no-cache"; 
        Response.AppendHeader("Pragma", "No-Cache"); 
        //将验证码图片写入内存流，并将其以 "image/Png" 格式输出 
        MemoryStream ms = new MemoryStream(); 
        try 
        ...{ 
            bmp.Save(ms, ImageFormat.Png); 
            Response.ClearContent(); 
            Response.ContentType = "image/Png"; 
            Response.BinaryWrite(ms.ToArray()); 
        } 
        finally 
        ...{ 
            //显式释放资源 
            bmp.Dispose(); 
            g.Dispose(); 
        } 
    } 
}

使用方法如下：
新建名为 GenerateCheckCode.aspx 的文件，将上述代码拷贝到代码文件 GenerateCheckCode.aspx.cs 
在需要验证码的地方放置语句 <asp:Image ID="img1" runat="server" ImageUrl="~/GenerateCheckCode.aspx" /> 即可。
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