要實現圖片的分段加載和顯示，可以通過以下步驟來實現：

1. 將圖片分成多個小塊，并分別加載到PictureBox控件中。
2. 在PictureBox控件中設置顯示區域，只顯示部分小塊圖片。
3. 隨著用戶滾動或拖動圖片，動態加載和顯示相應的小塊圖片。

以下是一個示例代碼，演示如何實現圖片的分段加載和顯示：

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

namespace PictureBoxLoadImageSegment
{
    public partial class Form1 : Form
    {
        private List<Image> imageSegments = new List<Image>();
        private int segmentWidth = 100;
        private int segmentHeight = 100;
        private int totalSegmentsX;
        private int totalSegmentsY;

        public Form1()
        {
            InitializeComponent();

            LoadImageSegments();
        }

        private void LoadImageSegments()
        {
            Image originalImage = Image.FromFile("image.jpg");
            totalSegmentsX = originalImage.Width / segmentWidth;
            totalSegmentsY = originalImage.Height / segmentHeight;

            for (int y = 0; y < totalSegmentsY; y++)
            {
                for (int x = 0; x < totalSegmentsX; x++)
                {
                    Bitmap segment = new Bitmap(segmentWidth, segmentHeight);
                    using (Graphics g = Graphics.FromImage(segment))
                    {
                        Rectangle sourceRect = new Rectangle(x * segmentWidth, y * segmentHeight, segmentWidth, segmentHeight);
                        g.DrawImage(originalImage, 0, 0, sourceRect, GraphicsUnit.Pixel);
                    }
                    imageSegments.Add(segment);
                }
            }

            originalImage.Dispose();
        }

        private void pictureBox1_Paint(object sender, PaintEventArgs e)
        {
            int startX = pictureBox1.AutoScrollPosition.X / segmentWidth;
            int startY = pictureBox1.AutoScrollPosition.Y / segmentHeight;

            int visibleSegmentsX = pictureBox1.ClientSize.Width / segmentWidth + 1;
            int visibleSegmentsY = pictureBox1.ClientSize.Height / segmentHeight + 1;

            for (int y = startY; y < Math.Min(startY + visibleSegmentsY, totalSegmentsY); y++)
            {
                for (int x = startX; x < Math.Min(startX + visibleSegmentsX, totalSegmentsX); x++)
                {
                    int index = y * totalSegmentsX + x;
                    if (index < imageSegments.Count)
                    {
                        e.Graphics.DrawImage(imageSegments[index], x * segmentWidth, y * segmentHeight);
                    }
                }
            }
        }
    }
}

在上面的示例代碼中，首先將圖片加載并分成多個小塊，然后在PictureBox的Paint事件中根據滾動位置和可見區域動態加載和顯示相應的小塊圖片。通過這種方式，可以實現圖片的分段加載和顯示功能。