这是应一个网友的问题而做的一个小程序，可以保存为位图，我觉得还是有一定的参考价值的，所以就把相关代码贴了出来 。

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

namespace HandImage
{
    public partial class frmTest : Form
    {
        List HandTrack=new List();
        public Graphics pb_Graphics;
        Bitmap pb_BMP = new Bitmap(239,235);

        int index = 0;    //第几笔
        public frmTest()
        {
            InitializeComponent();
        }

        private void pnlBar_MouseMove(object sender, MouseEventArgs e)
        {
            HandTrack[index].PT.Add(new Point(e.X, e.Y));
            pnlBar.Refresh();
        }

        private void pnlBar_Paint(object sender, PaintEventArgs e)
        {
            pb_Graphics = Graphics.FromImage((System.Drawing.Image)pb_BMP);
            pb_Graphics.Clear(pnlBar.BackColor);
            foreach(Points item in  HandTrack)
            {
                pb_Graphics.DrawLines(new Pen(Color.Black), item.PT.ToArray());  
            }
            e.Graphics.DrawImage(pb_BMP, 0, 0);
            pb_Graphics.Dispose(); 
        }

        class Points
        {
            public List PT=new List();
        }

        private void btnClear_Click(object sender, EventArgs e)
        {
            index = 0;
            HandTrack = new List();
            pnlBar.Refresh();  
        }

        private void pnlBar_MouseUp(object sender, MouseEventArgs e)
        {
            index++;
        }

        private void pnlBar_MouseDown(object sender, MouseEventArgs e)
        {
            HandTrack.Add(new Points());
            HandTrack[index].PT.Add(new Point(e.X, e.Y));
            pnlBar.Refresh();  
        }

        private void btnSave_Click(object sender, EventArgs e)
        {
            dlgSaveFile.Filter = "位图(*.bmp)|*.bmp"; 
            if (dlgSaveFile.ShowDialog() == DialogResult.OK)
            {
                string strFile = dlgSaveFile.FileName;
                pb_BMP.Save(strFile, System.Drawing.Imaging.ImageFormat.Bmp); 
            }
        }
    }
}