C# App WebDevHobo StackOverflow

using System.Windows.Forms;
using System.IO;
using System.Collections.Generic;


namespace SizeComparer {
    public partial class Form1 : Form {

        private string origFolder = string.Empty;
        private string shrunkFolder = string.Empty;
        private List<string> origFiles;
        private List<string> shrunkFiles;

        private FileInfo shrunkFileInfo;
        private FileInfo origFileInfo;
        private DirectoryInfo dirOrig;
        private DirectoryInfo dirShrunk;

        public Form1() {
            InitializeComponent();
            this.folderBrowseOriginal.ShowNewFolderButton = false;
            this.origFiles = new List<string>();
            this.shrunkFiles = new List<string>();
        }

        private void originalButton_Click(object sender, System.EventArgs e) {
            DialogResult dr = this.folderBrowseOriginal.ShowDialog();
            if(DialogResult.OK == dr) {
                this.origFolder = this.folderBrowseOriginal.SelectedPath;
                this.dirOrig = new DirectoryInfo(this.origFolder);
                this.fillList(this.dirOrig, this.origFiles);
            }
        }

        private void shrunkButton_Click(object sender, System.EventArgs e) {
            DialogResult dr = this.folderBrowseShrunk.ShowDialog();
            if(DialogResult.OK == dr) {
                this.shrunkFolder = this.folderBrowseShrunk.SelectedPath;
                this.dirShrunk = new DirectoryInfo(this.shrunkFolder);
                this.fillList(this.dirShrunk, this.shrunkFiles);
            }
        }

        private void fillList(DirectoryInfo dir, List<string> list) {
            foreach(FileInfo fi in dir.GetFiles("*.jpg")) {
                list.Add(fi.FullName);
            }
            foreach(FileInfo fi in dir.GetFiles("*.png")) {
                list.Add(fi.FullName);
            }
            foreach(FileInfo fi in dir.GetFiles("*.gif")) {
                list.Add(fi.FullName);
            }
        }

        private void copyButton_Click(object sender, System.EventArgs e) {
            int fileIndex = 0;
            string origFile = string.Empty;

            foreach(string shrunk in this.shrunkFiles) {
                fileIndex = this.origFiles.IndexOf(shrunk.Replace("\\Test",""));

                if(fileIndex == -1) {
                    continue;
                } else {
                    origFile = this.origFiles[fileIndex];
                }

                this.shrunkFileInfo = new FileInfo(shrunk);
                this.origFileInfo = new FileInfo(origFile);

                if(this.shrunkFileInfo.Length < this.origFileInfo.Length) {
                    File.Replace(shrunk, origFile, @"C:\Temp\tempfile");
                }
            }
        }

    }
}