Crop area selection control(like photoshop's) in c# windows form

how to develop a crop selection control like photoshop's in c# 4.0 in widows form application.

I have a windows form application in c# 4.0 that can crop images. At first you have to draw a rectangle using mouse to select the cropped region.

private Point _pt;
private Point _pt2;
private void picBoxImageProcessing_MouseDown(object sender, MouseEventArgs e)
{

if (e.Button == MouseButtons.Left)
{
int ix = (int)(e.X / _zoom);
int iy = (int)(e.Y / _zoom);

//reset _pt2
_pt2 = new Point(0, 0);
_pt = new Point(ix, iy);

// pictureBox1.Invalidate();
picBoxImageProcessing.Invalidate();
}
}

private void picBoxImageProcessing_MouseUp(object sender, MouseEventArgs e)
{
if (e.Button == MouseButtons.Left && _selecting)
{
_selecting = false;
}
}

private void picBoxImageProcessing_Paint(object sender, PaintEventArgs e)
{


if (_selecting &&_pt.X >= 0 && _pt.Y >= 0 && _pt2.X >= 0 && _pt2.Y >= 0)
{

e.Graphics.DrawRectangle(pen, _pt.X * _zoom, _pt.Y * _zoom,
(_pt2.X - _pt.X) * _zoom, (_pt2.Y - _pt.Y) * _zoom);
}
}

private void picBoxImageProcessing_MouseMove(object sender, MouseEventArgs e)
{


if (e.Button == MouseButtons.Left)
{
_selecting = true;
int ix = (int)(e.X / _zoom);
int iy = (int)(e.Y / _zoom);

_pt2 = new Point(ix, iy);

// pictureBox1.Invalidate();
picBoxImageProcessing.Invalidate();
}
}

there is no problem to draw the rectangle by mouse dragging. But if i want to change the height or width of the rectangle then I have to draw a new rectangle, that i don't want. I want to change the height and width of the rectangle by modifying the drawn rectangle instead of drawing a new rectangle.

I don't want to know how to crop. I need to draw a resizable rectangle on the image as we can do in photoshop.

So I need a crop selection control like photoshop's crop control.