public void ProcessRequest(HttpContext context)
{
context.Response.ContentType = "image/jpeg";
//創建位圖，并且給指定邊框的寬高
using (Image img=new Bitmap(80,25))
{

//創建畫家對象，在img對象畫字符串
using (Graphics g=Graphics.FromImage(img))
{
//設置位圖的背景顏色，默認是黑色
g.Clear(Color.White);
//設置驗證碼的寬高, img.Width-1, img.Height-1主要是背景顏色覆蓋了邊框線
g.DrawRectangle(Pens.Black, 0, 0, img.Width-1, img.Height-1);
//傳100個噪點，傳畫家對象，位圖對象
DrawPoint(100, g, img);
//畫4個驗證碼的字符串
string vcode=GetCode(4);//vcode這里可以賦值給Cookie

g.DrawString(vcode,
new Font("Arial", 14, FontStyle.Strikeout | FontStyle.Strikeout), // FontStyle字體的樣式，多個樣式，需要|線

Brushes.Black,
new RectangleF(r.Next(20), r.Next(7), img.Width, img.Height));
img.Save(context.Response.OutputStream, System.Drawing.Imaging.ImageFormat.Jpeg);//保存驗證碼對象，指定是Jpeg格式

}
}
}

//畫噪點方法

void DrawPoint(int point,Graphics g,Image img)
{
for (int i = 0; i < point; i++)
{
int x = r.Next(img.Width);
int y = r.Next(img.Width);
g.DrawLine(Pens.Red,
new Point(x, y),
new Point(x+2, y+2));

}
}

//隨機數
Random r = new Random();

//畫字符創
string GetCode(int point)
{
string txtStr = "ASF2345WE5R9F3HMBCZ455K";//這里的string字符串將會轉成 char數組，阿拉伯數字1和小寫字母l最好別寫在里面，會搞胡亂。
char[] charArr = txtStr.ToArray();
int num = 0;
string code = "";
for (int i = 0; i <point; i++)
{
num = r.Next(charArr.Length);
code +=charArr[num];
}
return code;
}