private string _title;
private Point _ps = new Point(-1, -1);
private Point _pe = new Point(-1, -1);

public TouchForm()
{
    InitializeComponent();
    _title = Text;
}

private void pic_MouseLeave(object sender, EventArgs e)
{
    Text = _title;
}

private void pic_MouseDown(object sender, MouseEventArgs e)
{
    _ps.X = e.X; _ps.Y = e.Y;
    _pe.X = -1;  _pe.Y = -1;
    SetTitle(new Point(e.X, e.Y));
}

private void pic_MouseUp(object sender, MouseEventArgs e)
{
    _pe.X = e.X; _pe.Y = e.Y;
    SetTitle(new Point(e.X, e.Y));
}

private void pic_MouseMove(object sender, MouseEventArgs e)
{
    SetTitle(new Point(e.X, e.Y));
}

private void SetTitle(Point i)
{
    var text = $"{_title}";

    if (-1 < i.X)
    {
        CalcPos(i, out Point o);
        text += $" - 現在 X:{o.X} Y:{o.Y}";
    }
    if (-1 < _ps.X)
    {
        CalcPos(_ps, out Point o);
        text += $" - 開始 X:{o.X} Y:{o.Y}";
    }
    if (-1 < _pe.X)
    {
        CalcPos(_pe, out Point o);
        text += $" - 終了 X:{o.X} Y:{o.Y}";
    }

    Text = text;
}

private void CalcPos(Point i, out Point o)
{
    if (radLT.Checked)
    {
        o = new Point(i.X, i.Y);
    }
    else if (radLB.Checked)
    {
        o = new Point(i.X, Math.Abs(i.Y - pic.Height));
    }
    else if (radRT.Checked)
    {
        o = new Point(Math.Abs(i.X - pic.Width), i.Y);
    }
    else
    {
        o = new Point(Math.Abs(i.X - pic.Width), Math.Abs(i.Y - pic.Height));
    }
}

コントロール上のマウス座標を取得（未整理）

コントロール配置

ソースコード