Drawing a circle on an image

Thank you for your answer...it's working

This will draw an ellipse from center point
public partial class Form1 : Form
{
bool _mouseDown = false;
Point origPt, newPt,centerPt;
int rectWidth, rectHeight;
Rectangle ellipseRect,clearRect;
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
}
private void pcbImage_Paint(object sender, PaintEventArgs e)
{
if (ellipseRect !=null)
{
e.Graphics.DrawEllipse(Pens.Red, ellipseRect);
}
}
private void pcbImage_MouseDown(object sender, MouseEventArgs e)
{
_mouseDown = true;
centerPt.X = e.X;
centerPt.Y = e.Y;
}
private void pcbImage_MouseMove(object sender, MouseEventArgs e)
{
if (_mouseDown == true)
{
newPt.X = e.X;
newPt.Y = e.Y;
Graphics g = pcbImage.CreateGraphics(); // draw temp ellipse
clearRect = Rectangle.Inflate(ellipseRect, 5, 5); //erase old ellipse
Region rg = new Region(clearRect); //erase old ellipse
pcbImage.Invalidate(rg); //erase old ellipse
rectWidth = Math.Abs(centerPt.X - newPt.X);// calculate half width of ellipse
rectHeight = Math.Abs(centerPt.Y - newPt.Y);// calculate half height of ellipse
origPt.X = centerPt.X - rectWidth;
origPt.Y = centerPt.Y - rectHeight;
ellipseRect = new Rectangle(origPt.X, origPt.Y, (rectWidth*2),(rectHeight *2));
g.DrawEllipse(Pens.Red, ellipseRect); // draw temp ellipse

}
}
private void pcbImage_MouseUp(object sender, MouseEventArgs e)
{
_mouseDown = false;
}
}

sorry I didn't explain myself, but I want to draw by hand that circle on that image...now I am using this code to draw with the function

e.Graphics.DrawPath


This is the code what does the drawing, I also have a button(btnLoad) and a pictureBox(pcbImage) where the image is loaded
Code:

namespace WindowsFormsApplication1
{
    public partial class frmMain : Form
    {
        private System.Drawing.Brush m_objBrush;
        private Graphics m_objGraphics;
        private Point lastPoint = Point.Empty;
        private System.Drawing.Drawing2D.GraphicsPath mousePath;
        private int mouseX, mouseY;
        Point mouseDownLocation;

        public frmMain()
        {
            mousePath = new System.Drawing.Drawing2D.GraphicsPath();

            InitializeComponent();
        }

        private void btnQuit_Click(object sender, EventArgs e)
        {
            Application.Exit();
        }

        private void frmMain_Load(object sender, EventArgs e)
        {
            m_objGraphics = this.CreateGraphics();
        }

        private void pcbImage_MouseDown(object sender, MouseEventArgs e)
        {
             mouseDownLocation = new Point(e.X, e.Y);
             mousePath.StartFigure();
             pcbImage.Focus();
             pcbImage.Invalidate();
        }

        private void pcbImage_MouseUp(object sender, MouseEventArgs e)
        {
            pcbImage.Invalidate();
        }

        private void pcbImage_MouseMove(object sender, MouseEventArgs e)
        {
           
             mouseX = e.X;
             mouseY = e.Y;
             if (e.Button == MouseButtons.Left && e.Button == Button.MouseButtons)
             {
                 mousePath.AddLine(mouseX, mouseY, mouseX, mouseY);
                 pcbImage.Invalidate();
             }
        }

        private void pcbImage_Paint(object sender, PaintEventArgs e)
        {
            e.Graphics.DrawPath(System.Drawing.Pens.Red, mousePath);
        }

    }
}

try this
private void pictureBox1_Paint(object sender, PaintEventArgs e)
{
e.Graphics.DrawEllipse(Pens.Red, 10, 10, 100, 100);
// e.Graphics.DrawEllipse(Pens.Red, X, Y, width, height);
}
draws a circle 10 pixels across and 10 pixels down from top left corner of picturebox, with a diameter of 100 pixels