#region 实现一个验证码的类

　　public class ValidateCode

　　{

　　private Bitmap validateimage;

　　private Graphics g;

　　public ValidateCode()

　　{

　　validateimage = new Bitmap(120, 30, PixelFormat.Format24bppRgb);

　　g = Graphics.FromImage(validateimage);

　　}

　　public void DrawValidateCode(Page e, string i)

　　{

　　g.DrawString(i, new Font("黑体",16,FontStyle.Bold),new SolidBrush(Color.White),new PointF(2,4));

　　g.FillRectangle(new LinearGradientBrush(new Point(0,0), new Point(120,30), Color.FromArgb(0,0,0,0),Color.FromArgb(255,255,255,255)),0,0,120,30);

　　//validateimage.Save(e.OutputStream, );

　　g.Save();

　　MemoryStream ms=new MemoryStream();
);

　　e.Response.ClearContent();

　　e.Response.ContentType="image/gif";

　　e.Response.BinaryWrite(ms.ToArray());

　　e.Response.End();
"), );

　　//e.End();

　　}

　　}

　　

　　#endregion

　　private void MakeValidateCode()

　　{

　　char[] s = new char[]{"0","1", "2","3","4","5","6","7","8","9","a"

　　,"b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q"

　　,"r","s","t","u","v","w","x","y","z","A","B","C","D","E","F","G"

　　,"H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","W"

　　,"X","Y","Z"};

　　string num = "";

　　Random r = new Random();

　　for(int i = 0; i < 5; i++)

　　{

　　num += s[r.Next(0, s.Length)].ToString();

　　}

　　((LoginUserInfo)Session["LoginUserInfo"]).ValidateNum = num;

　　TextBox3.Text = "";

　　}

　　调用上面的类即可成功检测验证码．