c# winform pictureBox怎么突出显示

c# winform pictureBox如何突出显示
我按顺序4*4排了16个pictureBox，紧挨着

我现在想选中哪个pictureBox，就给哪个pictureBox突出显示，以告诉用户，你选择的是XX pictureBox

我开始想选中哪个pictureBox就给哪个边框换一种颜色，可惜不会做，然后又想稍微的把选中的pictureBox放大一圈，结果放大了也看不出效果，好象放大的部位被其它pictureBox给压住了

请问还能怎么做可以突出pictureBox，方便用户知道选择了哪个pictureBox

我的16个pictureBox都指向了同一个方法

C# code

private void pictureBox1_Click(object sender, EventArgs e){    MessageBox.Show((sender as PictureBox).Name);}

C# code

        PictureBox old = null;        private void pictureBox2_Click(object sender, EventArgs e)        {            PictureBox p = (PictureBox)sender;            if (p == old) return;            if (old != null)            {                old.Width -= 10;                old.Height -= 10;                old.Location = new Point(old.Location.X + 5, old.Location.Y + 5);            }            old = p;            p.Width += 10;            p.Height += 10;            p.Location = new Point(p.Location.X - 5, p.Location.Y - 5);            p.BringToFront();                   }        private void pictureBox2_Paint(object sender, PaintEventArgs e)        {            PictureBox p = (PictureBox)sender;            if (p == old)            {                Pen pp = new Pen(Color.Red);                e.Graphics.DrawRectangle(pp, e.ClipRectangle.X, e.ClipRectangle.Y, e.ClipRectangle.X + e.ClipRectangle.Width - 1, e.ClipRectangle.Y + e.ClipRectangle.Height - 1);            }        }