ASP.NET中自动生成验证码

<span style="font-size: 18px;">可分为两个部分：</span><span style="color: rgb(51, 51, 51); font-family: Simsun; font-size: 18px; line-height: 26px;">一个生成四位随机数，一部分是绘制背景</span>

<span style="color: rgb(51, 51, 51); font-family: Simsun; font-size: 18px; line-height: 26px;">
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//自动生成验证码
private string GenerateCheckCode()
{
int number;
char code;
string checkCode = String.Empty;

//随机数
Random random = new Random();

//循环生成四位
for (int i = 0; i < 4; i++)
{
//自动生成随机数号码
number = random.Next();

code = (char)('0' + (char)(number % 10));

//累加四位随机数
checkCode += code.ToString();
}

Response.Cookies.Add(new HttpCookie("CheckCode", checkCode));

return checkCode;
}

//绘制验证码图片框
private void CreateCheckCodeImage(string checkCode)
{
if (checkCode == null || checkCode.Trim() == String.Empty)
return;
//自动画位图
System.Drawing.Bitmap image = new System.Drawing.Bitmap((int)Math.Ceiling((checkCode.Length * 12.5)), 22);
Graphics g = Graphics.FromImage(image);

try
{
//生成随机生成器
Random random = new Random();

//清空图片背景色
g.Clear(Color.White);

//画图片的背景噪音线
for (int i = 0; i < 2; i++)
{
int x1 = random.Next(image.Width);
int x2 = random.Next(image.Width);
int y1 = random.Next(image.Height);
int y2 = random.Next(image.Height);

g.DrawLine(new Pen(Color.Black), x1, y1, x2, y2);
}

Font font = new System.Drawing.Font("Arial", 12, (System.Drawing.FontStyle.Bold));
System.Drawing.Drawing2D.LinearGradientBrush brush = new System.Drawing.Drawing2D.LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2f, true);
g.DrawString(checkCode, font, brush, 2, 2);

//画图片的前景噪音点
for (int i = 0; i < 100; i++)
{
int x = random.Next(image.Width);
int y = random.Next(image.Height);

image.SetPixel(x, y, Color.FromArgb(random.Next()));
}

//画图片的边框线
g.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1);

System.IO.MemoryStream ms = new System.IO.MemoryStream();
image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
Response.ClearContent();
Response.ContentType = "image/Gif";
Response.BinaryWrite(ms.ToArray());
}
finally
{
g.Dispose();
image.Dispose();
}
}