public partial class Form1 : Form
{
    Bitmap bitmap = new Bitmap(@"c:\temp\penguins.jpg");
    RectangleF sourceRectange;
    Point lastMouseDown;
    Point lastMouseMove;
    public Form1()
    {
        InitializeComponent();
    }
    protected override void OnMouseDown(MouseEventArgs e)
    {
        this.lastMouseDown = this.lastMouseMove = e.Location;
    }
    protected override void OnMouseMove(MouseEventArgs e)
    {
        if( !this.Capture) return;
        DrawReversibleFrame();
        lastMouseMove = e.Location;
        DrawReversibleFrame();
    }
    protected override void OnMouseUp(MouseEventArgs e)
    {
        if (e.Button == System.Windows.Forms.MouseButtons.Left)
        {
            float l = sourceRectange.Left + sourceRectange.Width * lastMouseDown.X / this.ClientRectangle.Width;
            float t = sourceRectange.Top + sourceRectange.Height * lastMouseDown.Y / this.ClientRectangle.Height;
            float r = sourceRectange.Left + sourceRectange.Width * e.X / this.ClientRectangle.Width;
            float b = sourceRectange.Top + sourceRectange.Height * e.Y / this.ClientRectangle.Height;
            sourceRectange = RectangleF.FromLTRB(l, t, r, b);
        }
        else
        {
            this.sourceRectange = new RectangleF(PointF.Empty, bitmap.Size);
        }
        DrawReversibleFrame();
        this.Invalidate();
    }
    protected override void OnPaint(PaintEventArgs e)
    {
        if ( Math.Abs(sourceRectange.Width * sourceRectange.Height) < 1) sourceRectange = new RectangleF(PointF.Empty, bitmap.Size);
        e.Graphics.DrawImage(bitmap, (RectangleF)ClientRectangle, sourceRectange, GraphicsUnit.Pixel);
    }
    private void DrawReversibleFrame()
    {
        Rectangle rect = this.RectangleToScreen(Rectangle.FromLTRB(lastMouseMove.X, lastMouseMove.Y, lastMouseDown.X, lastMouseDown.Y));
        ControlPaint.DrawReversibleFrame(rect, Color.Cyan, FrameStyle.Dashed);
    }
}

------解决方案--------------------
http://blog.csdn.net/happy09li/article/details/7056567

参考

------解决方案--------------------
this.invaldate(true);  里面最好加个true参数