Principal.cs

using System;
using System.Drawing;
using System.Windows.Forms;

namespace R808ImagenVistaReducida
{
    public partial class Principal : Form
    {
        private Image imagenVistaRedida;

        public Principal()
        {
            InitializeComponent();
        }

        private void Principal_Load(object sender, EventArgs e)
        {
            using (Image imagen = Image.FromFile(@"Resources\VisualStudio-Logo.jpg"))
            {
                int anchoVistaReducida = 0;
                int altoVistaReducida = 0;

                if (imagen.Width > imagen.Height)
                {
                    anchoVistaReducida = 200;
                    altoVistaReducida = Convert.ToInt32(((200F / imagen.Width) * imagen.Height));
                }
                else
                {
                    altoVistaReducida = 200;
                    anchoVistaReducida = Convert.ToInt32(((200F / imagen.Height) * imagen.Width));
                }

                imagenVistaRedida = imagen.GetThumbnailImage(anchoVistaReducida, altoVistaReducida, null, IntPtr.Zero);
            }
        }

        private void Principal_Paint(object sender, PaintEventArgs e)
        {
            e.Graphics.DrawImage(imagenVistaRedida, 10, 10);
        }
    }
}