ASP. NET implementation of simple digital Verification code example

Call

CAPTCHA: <input type= "text" id= "txtvalidate" style= "Border:solid 1px #9B9B9B; width:85px;                        height:17px; "/>  

Background implementation
Rnd.aspx.cs

Using system;using system.collections;using system.configuration;using system.data;using System.Web;using System.web.security;using system.web.ui;using system.web.ui.htmlcontrols;using System.Web.UI.WebControls;using System.web.ui.webcontrols.webparts;using system.drawing;using System.drawing.imaging;public partial class Rnd: system.web.ui.page{private int codelen = 5;//randomly displays the number of characters private int fineness = 100;//picture clarity private int imgwidth =  65;//picture width private int imgheight = 20;//picture height private string fontFamily = "Roman";//font name private int fontSize = 12;    Font size private random random = new random ();        protected void Page_Load (object sender, EventArgs e) {string validatecode = Createvalidatecode ();        session["Randomnumber"] = Validatecode;        Bitmap Bitmap = new Bitmap (ImgWidth, imgheight);        Disturbbitmap (bitmap);        Drawvalidatecode (bitmap, Validatecode); Bitmap.    Save (Response.outputstream, imageformat.gif); } private String CreAtevalidatecode ()//Get random number {string validatecode = ""; for (int i = 0; i < Codelen; i++) {int n = random.        Next (10);//returns a less than maximum worth of random number validatecode + = n.tostring ();    } return Validatecode; The private void Disturbbitmap (Bitmap Bitmap)//Gets the background image {for (int i = 0; i < Bitmap. Width; i++) {for (int j = 0; J < bitmap. Height; J + +) {if (random. Next (<= this.fineness) {bitmap. SetPixel (i, J, color.white);//Gets the pixel color of the specified position}}}} private void Drawvalidatecode (Bit        Map Bitmap, String validatecode) {Graphics g = graphics.fromimage (bitmap);        Font font = new Font (fontFamily, fontSize, fontstyle.bold); g.DrawString (Validatecode, Font, Brushes.green, random.) Next ( -3, one), random. Next (-4, 1));//Draw text characters in the specified area}}