2.登录验证码（代码）

 <td style="width:120px;padding-left:0px;">
<img id="imgVCode" src="/VCode.ashx" style="cursor:pointer;" />
</td>

/// <summary>
/// VCode 的摘要说明
/// </summary>
public class VCode : IHttpHandler, IRequiresSessionState
{
/// <summary>
/// 验证码 存入Session 的 键
/// </summary>
public const string vCodeName = "vcode";

HttpContext context;

public void ProcessRequest(HttpContext context)
{
this.context = context;
//1.0 生成验证码字符串
string strVCode = GenerateCheckCode();
//1.1保存到 Session 中
context.Session[vCodeName] = strVCode;
//2.0 绘制验证码图片 输出到浏览器
CreateCheckCodeImage(strVCode);
}

#region 1.0 生成随机验证码方法 -string GenerateCheckCode()
/// <summary>
/// 生成随机验证码方法
/// </summary>
/// <returns></returns>
private string GenerateCheckCode()
{
int number;
char code;
string checkCode = String.Empty;

System.Random random = new Random();

for (int i = 0; i < 5; i++)
{
number = random.Next();

if (number % 2 == 0)
code = (char)('0' + (char)(number % 10));
else
code = (char)('0' + (char)(number % 10));
//code = (char)('A' + (char)(number % 26));

checkCode += code.ToString();
}
return checkCode;
}
#endregion

#region 2.0 生成验证吗图片，并返回浏览器 -void CreateCheckCodeImage(string checkCode)
/// <summary>
/// 2.0 生成验证吗图片，并返回浏览器
/// </summary>
/// <param name="checkCode"></param>
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);
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 < 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.Silver), 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, 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);
context.Response.ClearContent();
context.Response.ContentType = "image/Gif";
context.Response.BinaryWrite(ms.ToArray());
}
finally
{
g.Dispose();
image.Dispose();
}
}
#endregion

public bool IsReusable
{
get
{
return false;
}
}
}
}