在pictureBox上每次只绘制一个矩形框，绘制下一个矩形框时上次绘制的矩形框取消，代码如链接：https://www.cnblogs.com/luxiao/p/5625196.html
在绘制矩形框时要在程序中添加鼠标相应的事件MouseDown、MouseUp、MouseMove、Paint。
绘制矩形框的代码如下：
1 Point start, end;//绘制矩形框的起点和终点 2 bool blnDraw;//在MouseMove事件中判断是否绘制矩形框 3 public struct StartAndEndPoint 4 { 5 Point Start; 6 Point End; 7 } 8 //绘制矩形起始点和终止点的集合 9 List<StartAndEndPoint> multiAreaPoint=new List<StartAndEndPoint>(); 10 11 private void pic_MouseDown(object sender, MouseEventArgs e) 12 { 13 if (e.Button == MouseButtons.Left) 14 { 15 start = e.Location; 16 blnDraw = true; 17 } 18 // 点击鼠标右键绘制整个pictureBox区域 19 if (e.Button == MouseButtons.Right) 20 { 21 start = new Point(0, 0); 22 } 23 } 24 25 private void pic_MouseUp(object sender, MouseEventArgs e) 26 { 27 PictureBox pic = sender as PictureBox; 28 29 if (e.Button == MouseButtons.Left) 30 { 31 end = e.Location; 32 blnDraw = false; 33 } 34 if (e.Button == MouseButtons.Right) 35 { 36 end = new Point(pic.Width, pic.Height); 37 } 38 39 40 if (pic.Image != null) 41 { 42 if (start != end) 43 { 44 StartAndEndPoint onepoint = new StartAndEndPoint(); 45 onepoint.start = start; 46 onepoint.end = end; 47 48 if ((!multiAreaPoint.Contains(onepoint))) 49 { 50 multiAreaPoint.Add(onepoint);//添加不同区域起始和终止点的结构体数组 51 } 52 } 53 } 54 55 //pic.Refresh(); 56 } 57 58 private void pic_MouseMove(object sender, MouseEventArgs e) 59 { 60 if (blnDraw) 61 { 62 if (e.Button != MouseButtons.Left)//判断是否按下左键 63 return; 64 end = e.Location; 65 pic.Invalidate(); 66 } 67 } 1 private void pic_Paint(object sender, PaintEventArgs e) 2 { 3 PictureBox pic = sender as PictureBox; 4 5 Pen pen = new Pen(Color.Red, 1); 6 pen.DashStyle = System.Drawing.Drawing2D.DashStyle.Dot;//绘制线的格式 7 if (blnDraw) 8 { 9 if (pic.Image != null) 10 { 11 //此处是为了在绘制时可以由上向下绘制，也可以由下向上绘制 12 e.Graphics.DrawRectangle(pen, Math.Min(start.X, end.X), Math.Min(start.Y, end.Y), Math.Abs(start.X - end.X), Math.Abs(start.Y - end.Y)); 13 } 14 } 15 16 //将之前绘制的矩形框再次绘制一遍 17 foreach (StartAndEndPoint points in multiAreaPoint) 18 { 19 Point p1 = points.start; 20 Point p2 = points.end; 21 e.Graphics.DrawRectangle(pen, Math.Min(p1.X, p2.X), Math.Min(p1.Y, p2.Y), Math.Abs(p1.X - p2.X), Math.Abs(p1.Y - p2.Y)); 22 } 23 24 pen.Dispose(); 25 } 绘制多个矩形框的原理是将多个起始点与终止点放到数组中，在调用Paint方法时，将这些点重新绘制一遍，那么取消绘制这些矩形就可以将数组中的点删除掉，在调用Paint方法就可以删除这些矩形啦！
代码如下：
1 multiAreaPoint.Clear(); 2 pic.Refresh();
pic.Refresh();是为了调用Paint方法。
若有不同见解或其他实现方法，欢迎与我交流。