一、水印

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

Graphics g = Graphics.FromImage(img);

 string s = "www.itnba.com";

Font f = new Font("黑体",130);

Brush b = new SolidBrush(Color.Red);

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

 Bitmap bit = new Bitmap(90, 40);//画布大小        Graphics g = Graphics.FromImage(bit);//创建绘制对象，告诉它往哪张图片上绘制        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);//画布颜色随机        for (int i = 0; i < 10; i++)//随机画干扰线        {            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";//设置随机的验证码，从里面抽取        int wei = 0;        for (int i = 0; i < 4; i++)//取四位验证码，颜色随机        {            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("黑体", w);            SolidBrush b = new SolidBrush(color2);            g.DrawString(m, f, b, wei, r.Next(0, 10));            wei += w;        }        Session["YZM"] = s;//把验证码保存到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();

验证码：<asp:TextBox ID="TextBox3" runat="server"></asp:TextBox>        <asp:Image ID="Image1" runat="server" ImageUrl="Default2.aspx" />