如何在不打开对话框的情况下按位置加密特定图像？

这是我用于加密和解密图像的简单程序。但我不想单击按钮并加密或解密特定图像。我想在form_load和中使用它form_closed。我的图片位置是C:\Users\Mateen\Downloads\MyImage.jpg。打开Form时，图像应解密并显示在图片框中；关闭Form时，图像应重新加密。

有人可以帮忙吗？

using System;
using System.IO;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
       private void EncryptFile()
        {            
            OpenFileDialog dialog = new OpenFileDialog();
            dialog.Filter = "JPG Files (*.jpg)|*.jpg|PNG Files (*.png)|*.png|JPEG Files (*.jpeg)|*.jpg|EXE Files (*.exe)|*.exe|GIF Files (*.gif)|*.gif";
            dialog.InitialDirectory = @"C:\Users\Mateen\Downloads\MyImage.jpg";
            dialog.Title = "Please select an image file to encrypt.";
            byte[] ImageBytes;
            if (dialog.ShowDialog() == DialogResult.OK)
            {
                ImageBytes = File.ReadAllBytes(dialog.FileName);

                for (int i = 0; i < ImageBytes.Length; i++)
                {
                    ImageBytes[i] = (byte)(ImageBytes[i] + 5);
                }

                File.WriteAllBytes(dialog.FileName, ImageBytes);
            }            
        }

        private void DecryptFile()
        {
            OpenFileDialog dialog = new OpenFileDialog();
            dialog.Filter = "JPG Files (*.jpg)|*.jpg|PNG Files (*.png)|*.png|JPEG Files (*.jpeg)|*.jpg|EXE Files (*.exe)|*.exe|GIF Files (*.gif)|*.gif";
            dialog.InitialDirectory = @"C:\Users\Mateen\Downloads\MyImage.jpg";
            dialog.Title = "Please select an image file to decrypt.";
            byte[] ImageBytes;
            if (dialog.ShowDialog() == DialogResult.OK)
            {
                ImageBytes = File.ReadAllBytes(dialog.FileName);

                for (int i = 0; i < ImageBytes.Length; i++)
                {
                    ImageBytes[i] = (byte)(ImageBytes[i] - 5);
                }

                File.WriteAllBytes(dialog.FileName, ImageBytes);
            }            
        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }

        private void Form1_FormClosed(object sender, FormClosedEventArgs e)
        {

        }

        private void button1_Click(object sender, EventArgs e)
        {
            EncryptFile();
        }

        private void button2_Click(object sender, EventArgs e)
        {
            DecryptFile();
        }
    }
}