水印、圖片驗證碼

（貌似這個驗證碼不能獲取，假設設置一個隱藏的label來記錄又失去了他的意義）

1、水印

1.畫布

 System.Drawing.Image img = System.Drawing.Image.FromStream(FileUpload1.FileContent);

2.建立繪製對象，告訴它往哪張圖片上繪製

Graphics g = Graphics.FromImage(img);

3.繪製的內容

 string s = "www.itnba.com";

4.繪製的字體

Font f = new Font("黑體",130);

5.繪製的畫刷

Brush b = new SolidBrush(Color.Red);

6.開始繪製

g.DrawString(s, f, b, 5, 5);

2、圖片驗證碼

 Bitmap bit = new Bitmap(90, 40);//畫布大小
        Graphics g = Graphics.FromImage(bit);//建立繪製對象，告訴它往哪張圖片上繪製
        Random r = new Random();
        string s = "";
        Color color1 = Color.FromArgb(r.Next(155, 255), r.Next(155, 255), r.Next(155, 255));
        g.FillRectangle(new SolidBrush(color1), 0, 0, 90, 40);//畫布顏色隨機
        for (int i = 0; i < 10; i++)//隨機畫干擾線
        {
            Color color3 = Color.FromArgb(r.Next(170, 255), r.Next(190, 255), r.Next(170, 255));
            Pen pp = new Pen(new SolidBrush(color3), r.Next(0, 5));
            g.DrawLine(pp, r.Next(0, 90), r.Next(0, 40), r.Next(0, 90), r.Next(0, 40));
        }
        

        string yan = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";//設置隨機的驗證碼，從裏面抽取
        int wei = 0;
        for (int i = 0; i < 4; i++)//取四位驗證碼，顏色隨機
        {
            string m = yan.Substring(r.Next(0, yan.Length), 1);
            s += m;
            Color color2 = Color.FromArgb(r.Next(0, 155), r.Next(0, 155), r.Next(0, 155));
            int w = r.Next(20, 25);
            Font f = new Font("黑體", w);
            SolidBrush b = new SolidBrush(color2);

            g.DrawString(m, f, b, wei, r.Next(0, 10));
            wei += w;
        }

        Session["YZM"] = s;//把驗證碼保存到session中
        for (int i = 0; i < 251; i++)
        {
            Color color3 = Color.FromArgb(r.Next(0, 255), r.Next(0, 255), r.Next(0, 255));
            Pen pp = new Pen(new SolidBrush(color3), r.Next(0, 5));
            int a = r.Next(0, 90);
            int b = r.Next(0, 40);
            g.DrawLine(pp, a, b, (a + 1), (b + 1));
        }


        bit.Save(Response.OutputStream, System.Drawing.Imaging.ImageFormat.Jpeg);
        Response.End();

驗證碼：<asp:TextBox ID="TextBox3" runat="server"></asp:TextBox>
        <asp:Image ID="Image1" runat="server" ImageUrl="Default2.aspx" />//這裏圖片路徑不是一張圖片的話會默認打開