putting 1 Picture box on the form and write this code
also you can change the the minus number beside of Width and Height to get best result
System.Drawing.Drawing2D.GraphicsPath gp = new System.Drawing.Drawing2D.GraphicsPath();
gp.AddEllipse(0, 0, pictureBox1.Width - 3, pictureBox1.Height - 3);
Region rg = new Region(gp);
pictureBox1.Region = rg;