ASP.Net(Self Maid Custom Captcha)

//Step:01 Create A Page With this function On Load

protected void Page_Load(object sender, EventArgs e)

    {

        Random num1 = new Random();

        int numQ1;

        int numQ2;

        int numQ3;

        int numQ4;

        int numQ5;

        int numQ6;

        string QString;

        numQ1 = num1.Next(97, 122);

        numQ2 = num1.Next(97, 122);

        numQ3 = num1.Next(48, 57);

        numQ4 = num1.Next(65, 90);

        numQ5 = num1.Next(48, 57);

        numQ6 = num1.Next(65, 90);

        QString = Char.ConvertFromUtf32(numQ1) + "" + Char.ConvertFromUtf32(numQ2) + "" + Char.ConvertFromUtf32(numQ3) + "" + Char.ConvertFromUtf32(numQ4) + Char.ConvertFromUtf32(numQ5) + Char.ConvertFromUtf32(numQ6);

        Session["SessionName"] = QString;

        Bitmap bitmap = new Bitmap(200, 60);

        Graphics Grfx = Graphics.FromImage(bitmap);

        Font font = new Font("Times New Roman", 35, FontStyle.Bold, GraphicsUnit.Pixel);

        Rectangle Rect = new Rectangle(0, 0, 200, 60);

        Grfx.FillRectangle(Brushes.White, Rect);

        Grfx.DrawRectangle(Pens.White, Rect);

        Grfx.DrawString(QString, font, Brushes.Black, 10, 7);

        Pen blackPen = new Pen(Color.Red, 2);

        // Create points that define line.

        Random r = new Random();

        int p1 = r.Next(0, 60);

        int p2 = r.Next(10, 155);

        Point point1 = new Point(p1, 60);

        Point point2 = new Point(155, p2);

        Point point3 = new Point(60, p1);

        Point point4 = new Point(p2, 155);

        // Draw line to screen.

        Grfx.DrawLine(blackPen, point1, point2);

        Grfx.DrawLine(blackPen, point3, point4);

       

        Point[] pnt = new Point[3];

        pnt[0] = new Point(r.Next(0,70), r.Next(0,70));

        pnt[1] = new Point(r.Next(37,70), r.Next(0,36));

        pnt[2] = new Point(r.Next(0,36), r.Next(0,35));

        Grfx.DrawCurve(blackPen, pnt);

        Response.ContentType = "Image/jpeg";

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

        bitmap.Dispose();

        Grfx.Dispose();

    }

//Step:02 Image Control To Show The Captcha

<asp:Label ID="lblCaptchaError" ForeColor="Red" Font-Italic="true" Font-Size="10" runat="server" Text=""></asp:Label>

<asp:Image ID="imageCaptcha" runat="server" ImageUrl="~/pageName.aspx" />
<asp:TextBox ID="txtCaptcha" runat="server"></asp:TextBox>
//ImageUrl= Page Name

//Step:03(a) Change Image New Image
<asp:LinkButton ID="lbtnNewCode" runat="server" OnClick="lbtnNewCode_Click">
Try a new code</asp:LinkButton>

//Step:03(b) Change Image New Image
protected void lbtnNewCode_Click(object sender, EventArgs e)

{

    imageCaptcha.ImageUrl = "pageName.aspx";

}

//Step:04(a) Captcha Validate

private bool ValidCaptcha()

    {

        if (Session["SessionName"] != null)
        {

            if (txtCaptcha.Text != Session["SessionName "].ToString())

            {

                lblCaptchaError.Text = "Invalid Captcha Text";

                return false;

            }

            else

            {

                lblCaptchaError.Text = "";

                return true;

            }

        }

        else

        {

            lblCaptchaError.Text = "Invalid Captcha Text";

            return false;

        }

    }

//Step:04(b) Button Click

protected void btn_Click(object sender, ImageClickEventArgs e)

    {

        try

        {

            lblError.Visible = false;

            if (txtCaptcha.Text != null)

            {

                if (ValidCaptcha())

                {

                    txtCaptcha.Text = string.Empty;

      

             //empty captcha text

                    Response.Redirect("~/YourPage.aspx");

                }

                else

                {

                    //empty captcha text

                    txtCaptcha.Text = string.Empty;

                }

            }

        }

        catch (Exception)

        {

            return;

        }