新建一个checkcode.aspx用于显示验证码。

重要代码如下：

private string GenerateCheckCode()//GenerateCheckCode方法生成验证码字符串。

{
int num;
char code;
string checkCode = string.Empty;
System.Random random = new Random();

for (int i = 0; i < 4; i++)//这里修改这个4为几就能使验证码的位数为几，本次仅仅测试，所以不做成通用效果。
{
num = random.Next();
if (num % 2 == 0)
{
code = (char)(‘0‘ + (char)(num % 10));
}
else
{
code = (char)(‘A‘ + (char)(num % 26));

}
checkCode += code.ToString();
}
Response.Cookies.Add(new HttpCookie("CheckCode", checkCode));
return checkCode;
}

CreateCheckCodeImg这个方法调用画布。

private void CreateCheckCodeImg(string checkCode)
{
if (checkCode == null || checkCode.Trim() == string.Empty)
return;
System.Drawing.Bitmap img = new System.Drawing.Bitmap((int)Math.Ceiling((checkCode.Length * 12.5)), 22);
Graphics g = Graphics.FromImage(img);
try
{

Random random = new Random(); //生成随机器
g.Clear(Color.White); //清空图片背景色
for (int i = 0; i < 2; i++) //画图片背景噪音线
{
int x1 = random.Next(img.Width);
int x2 = random.Next(img.Width);
int y1 = random.Next(img.Height);
int y2 = random.Next(img.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.FontStyle.Italic));
System.Drawing.Drawing2D.LinearGradientBrush brush = new System.Drawing.Drawing2D.LinearGradientBrush(new Rectangle(0, 0, img.Width, img.Height), Color.Blue, Color.DarkRed, 1.2f, true);
g.DrawString(checkCode, font, brush, 2, 2);

for (int i = 0; i < 100; i++)//画图片前景噪音点
{
int x = random.Next(img.Width);
int y = random.Next(img.Height);
img.SetPixel(x, y, Color.FromArgb(random.Next()));
}
//画图片边框线
g.DrawRectangle(new Pen(Color.Silver), 0, 0, img.Width - 1, img.Height - 1);
System.IO.MemoryStream ms = new System.IO.MemoryStream();
img.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
Response.ClearContent();
Response.ContentType = "image/Gif";
Response.BinaryWrite(ms.ToArray());
}
finally
{
g.Dispose();
img.Dispose();
}
}

如何调用？

在Login页面中适当位置加入图片咯。                    <img id="IMG1" runat="server" src="http://www.mamicode.com/checkcode.aspx" /></td>

ASP.NET尝试着做一个验证码。