C# move image from picturebox to another folder.

The system will display one image on PictureBox from the Upload folder(contains multiple images). After the user clicks on the pass button then it will move the current image that shows in the Picturebox from the Upload Folder to the Pass folder and it will go to the next images. When I clicked on the pass button there have no images move to the pass folder. May I know how to fix this thanks?

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.IO;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace WinFormsApp1
{
    public partial class Form4 : Form
    {
        DirectoryInfo latestSession = new DirectoryInfo(@"Upload\").GetDirectories().OrderByDescending(d => d.LastWriteTimeUtc).First();
        public Form4()
        {
            InitializeComponent();
        }

        //proceed to next image after pressing pass / fail button
        public void incrementImage()
        {
            nCurrentItem++;
            firstImage++;

            if (nCurrentItem > nTotalNumber)
                nCurrentItem = nTotalNumber;

            else if (nCurrentItem < nTotalNumber)
                using (var bmpTemp = new Bitmap(ImageFilenames[nCurrentItem]))
                {
                    PicBox.Image = new Bitmap(bmpTemp);
                }

            imgCounter.Text = firstImage.ToString() + " / " + nTotalNumber.ToString();
        }
        

        //load images
        int nTotalNumber = 0;
        int nCurrentItem = 0;
        int firstImage = 1;
        List<string> ImageFilenames = new List<string>();
        string uploadDir = Path.Combine(@"Upload\");
        

        private void uploadBtn_Click(object sender, EventArgs e)
        {
            using (OpenFileDialog open = new OpenFileDialog())
            {
                open.Multiselect = true;

                //set the initial directory to last modified folder
                open.InitialDirectory = latestSession.ToString();
                open.Filter = "Image Files(*.jpg; *.jpeg; *.gif; *.bmp;*.png)|*.jpg; *.jpeg; *.gif; *.bmp; *.png";
                if (open.ShowDialog() == DialogResult.OK)
                {
                    string sFileName = open.FileName;
                    ImageFilenames = open.FileNames.ToList();

                    using (var bmpTemp = new Bitmap(ImageFilenames[0]))
                    {
                        PicBox.Image = new Bitmap(bmpTemp);
                    }

                    //stretch images to the size of picbox
                    PicBox.SizeMode = PictureBoxSizeMode.StretchImage;
                }

            }
            if (ImageFilenames.Count > 0)
            {
                nTotalNumber = ImageFilenames.Count;
                ImageUploadCounter.Text = nTotalNumber.ToString();
                imgCounter.Text = firstImage.ToString() + " / " + nTotalNumber.ToString();

            }
        }

        private void button1_Click(object sender, EventArgs e)
        {
            Form6 fm = new Form6();
            fm.Show();
            this.Hide();
        }

        private void PassBtn_Click(object sender, EventArgs e)
        {
            string passFolder = Path.Combine(latestSession.ToString(), "Pass");

            try
            {
                File.Move(ImageFilenames[nCurrentItem], Path.Combine(passFolder, ImageFilenames[nCurrentItem]), true);
                incrementImage();
            }
            catch(Exception ex) { }

        }
    }
}