this.pictureBox1.MouseDown += new System.Windows.Forms.MouseEventHandler(this.pictureBox1_MouseDown);
private void pictureBox1_MouseDown(object sender, MouseEventArgs e)
{
Point aa = new Point(e.X, e.Y);
Rectangle r1 = new Rectangle(0, 0, this.pictureBox1.Width, ((int)this.pictureBox1.Height/2));
Rectangle r2 = new Rectangle(0, ((int)this.pictureBox1.Height / 2), this.pictureBox1.Width, ((int)this.pictureBox1.Height / 2));
if (r1.Contains(aa))
{
MessageBox.Show("r1");
}
if (r2.Contains(aa))
{
MessageBox.Show("r2");
}
}