face detection using emgucv library.

I don't know anything about the library you are using on face detection, but I think your problem is with the timer. Asign the tick event handler after the line of code capture = new Capture(0), because probably tick runs before you initialize capture

this.timer1.Tick += new System.EventHandler(this.timer1_Tick);

and remove the above line form designer...

or
set in designer Enabled = false
and in code after capture = new capture set it to enabled = true

This is an educated guess (given I have not met the EMGUCV library), but from what you say :
"I have used breakpoints to detect errors, it is going to the Haar line but it not entering in capture line capture= new capture(0)."
It would seem that creating a new HaarCascade does not return immediately, so you are not reaching the capture instance creation.

Since you are working in a timer, the way I would handle it is:
1) Remove the capture and cascade creation from the form constructor.
2) On the first timer tick, suspend the timer, display a "please wait" message and create the cascade. Re-enable the timer when the cascade is complete, and remove the message. Then create the capture instance and continue.

I can't check what should happen with teh cascade, because the EMGU CV website is not responding, but it should have samples there anyway. Have a look and see what they do.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Diagnostics;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using Emgu.CV;
using Emgu.CV.Structure;
using Emgu.Util;

namespace CameraCapture
{
    public partial class CameraCapture : Form
    {
        Image<Bgr, Byte> image;
        private Capture _capture;
        private bool _captureInProgress;

        public CameraCapture()
        {
            InitializeComponent();
        }

        private void ProcessFrame(object sender, EventArgs arg)
        {
            image = _capture.QueryFrame();

            Run();


            captureImageBox.Image = image;

        }
        public void Run()
        {

            Image<Gray, Byte> gray = image.Convert<Gray, Byte>(); //Convert it to Grayscale


            //normalizes brightness and increases contrast of the image
            gray._EqualizeHist();

            //Read the HaarCascade objects
           HaarCascade face = new HaarCascade("haarcascade_frontalface_alt_tree.xml");
             //HaarCascade eye = new HaarCascade("haarcascade_eye.xml");

            //Detect the faces  from the gray scale image and store the locations as rectangle
            //The first dimensional is the channel
            //The second dimension is the index of the rectangle in the specific channel
            MCvAvgComp[][] facesDetected = gray.DetectHaarCascade(
               face,
               1.1,
               10,
               Emgu.CV.CvEnum.HAAR_DETECTION_TYPE.DO_CANNY_PRUNING,
               new Size(20, 20));

            foreach (MCvAvgComp f in facesDetected[0])
            {
                //draw the face detected in the 0th (gray) channel with blue color
                image.Draw(f.rect, new Bgr(Color.Blue), 2);




            }


        }
        private void captureButtonClick(object sender, EventArgs e)
        {
            #region if capture is not created, create it now
            if (_capture == null)
            {
                try
                {
                    _capture = new Capture();
                }
                catch (NullReferenceException excpt)
                {
                    MessageBox.Show(excpt.Message);
                }
            }
            #endregion

            if (_capture != null)
            {
                if (_captureInProgress)
                {  //stop the capture
                    captureButton.Text = "Start Capture";
                    Application.Idle -= ProcessFrame;
                }
                else
                {
                    //start the capture
                    captureButton.Text = "Stop";
                    Application.Idle += ProcessFrame;
                }

                _captureInProgress = !_captureInProgress;
            }
        }

        private void ReleaseData()
        {
            if (_capture != null)
                _capture.Dispose();
        }
    }
}