private void pictureBoxPoints_MouseDown(object sender, MouseEventArgs e)
{
    if (pictureBoxPoints.Image != null)
    {
        pointCoordinates.X = e.X;
        pointCoordinates.Y = e.Y;

        // Convert point coordinates from pictureBoxPoints to original frame coordinates
        double xFactor = (double)pictureBoxPoints.Image.Width / pictureBoxPoints.Width;
        double yFactor = (double)pictureBoxPoints.Image.Height / pictureBoxPoints.Height;
        double xOffset = _convertedRectangle.X;
        double yOffset = _convertedRectangle.Y;

        int imageX = (int)(pointCoordinates.X * xFactor) + (int)xOffset;
        int imageY = (int)(pointCoordinates.Y * yFactor) + (int)yOffset;

        // Add the point to the list
        _points.Add(new System.Drawing.Point(imageX, imageY));

        using (Graphics g = Graphics.FromImage(bmp))
        {
            foreach (System.Drawing.Point point in _points)
            {
                g.DrawRectangle(Pens.Red, new System.Drawing.Rectangle(point.X, point.Y, 10, 10));
            }
        }

        bmp.Save(@"d:Converted.bmp");

        draw = true;

        pictureBoxPoints.Invalidate();
    }
}

private void pictureBoxPoints_Paint(object sender, PaintEventArgs e)
{
    e.Graphics.SmoothingMode = SmoothingMode.HighQuality;

    if (pictureBoxPoints.Image != null && draw)
    {
        foreach (System.Drawing.Point point in _points)
        {
            e.Graphics.FillEllipse(Brushes.Red,
                new Rectangle(pointCoordinates.X, pointCoordinates.Y, 10, 10));
        }
        draw = false;
    }
}

i keep the points in the list _points

i make instance to the list once at the top of form1:

private List<System.Drawing.Point> _points = new List<System.Drawing.Point>();

but each time i click with the mouse down it’s drawing a new point but delete the last one before. and i want to keep all the points drawn on the pictureBoxPoints.