有验证码的登陆界面（ajax,ashx技术制作）(2)

            Random rand = new Random();
            for (int i = 0; i < n; i++)
            {
                if (temp != -1)
                {
                    rand = new Random(i * temp * ((int)DateTime.Now.Ticks));
                }
                int t = rand.Next(CharArray.Length - 1);
                if (temp == t)
                {
                    return CreateRandomCode(n);
                }
                temp = t;
                randomCode += CharArray[t];
            }
            return randomCode;
        }

        private void CreateImage(string checkCode, HttpContext context)
        {
            int iwidth = (int)(checkCode.Length * 13);
            System.Drawing.Bitmap image = new System.Drawing.Bitmap(iwidth, 23);
            Graphics g = Graphics.FromImage(image);
            Font f = new System.Drawing.Font("Arial", 12, (System.Drawing.FontStyle.Italic | System.Drawing.FontStyle.Bold));

            // 前景色
            Brush b = new System.Drawing.SolidBrush(Color.Black);

            // 背景色
            g.Clear(Color.White);

            // 填充文字
            g.DrawString(checkCode, f, b, 0, 1);