How to draw a line in a loading image in a C# form??

Thank you Kirtan,

This code is under the "Load" button???

The code is
 
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace Lines
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Load_Click(object sender, EventArgs e)
        {
           
            try
            {

                OpenFileDialog open = new OpenFileDialog();

                open.Filter = "Image Files(*.jpg; *.jpeg; *.gif; *.bmp)|*.jpg; *.jpeg; *.gif; *.bmp";

                if (open.ShowDialog() == DialogResult.OK)
                {

                    pictureBox1.Image = new Bitmap(open.FileName);

                }

            }

            catch (Exception)
            {

                throw new ApplicationException("Failed loading image");

            }
        }

        private void Load_Paint(object sender, PaintEventArgs e)
        {
            Graphics g = pictureBox1.CreateGraphics();
            g.DrawLine(new Pen(new SolidBrush(Color.Red)), new Point(50, 50), new Point(200, 50));
        }

     }
   }

But this is not what i really want. The point is to load the image in picture Box and a drawline appears in the center of photo.
How do i  achieve that???

  private void button1_Click(object sender, EventArgs e)
        {

            Graphics g = pictureBox1.CreateGraphics();
            g.DrawLine(new Pen(new SolidBrush(Color.Red)), new Point(50, 50), new Point(200, 50));
        }