随机产生验证码

protected void Page_Load(object sender, EventArgs e)
{
this.CreateCheckCodeImage(GenerateCheckCode());
}
private string GenerateCheckCode()
{
int number;
char code;
string checkCode = string.Empty;

Random radom = new Random();

for (int i = 0; i < 6; i++)
{
number = radom.Next();
if (number % 2 == 0)
{
code = (char)('0' + (char)(number % 10));
}
else
{
code = (char)('A'+(char)(number%26));
}
checkCode += code.ToString();
}
Response.Cookies.Add(new HttpCookie("CheckCode",checkCode));
return checkCode;
}

private void CreateCheckCodeImage(string checkCode)
{
if (checkCode == null || checkCode.Trim() == String.Empty)
{
return;
}
System.Drawing.Bitmap image = new System.Drawing.Bitmap((int)Math.Ceiling(checkCode.Length*12.5),22);
System.Drawing.Graphics g = System.Drawing.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 < 25; 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.GreenYellow), x1, y1, x2, y2);
}

Font font = new System.Drawing.Font("Verdana", 12, (System.Drawing.FontStyle.Bold | System.Drawing.FontStyle.Italic));
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 < 80; 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.Red), 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();
}
}

<form id="form1" runat="server">
<div>
<asp:TextBox runat="server" ID="txt"></asp:TextBox>
<img src="pic.aspx" alt="点击更换图片!" onclick="this.src=this.src+'?'"/>
<br />
<asp:Button runat="server" ID="bt" onclick="bt_Click" Text="提交"/><asp:Label runat="server" ID="msg"></asp:Label>
</div>
</form>
//C#