Change Zigzag Border in Picturebox image in winform application

You can use the following code :
 

// Set the background image of the PictureBox
pictureBox1.BackgroundImage = Properties.Resources.myImage;

 
GraphicsPath path = new GraphicsPath();

 
AddZigZagToPath(path, pictureBox1.ClientRectangle, 10, 5);

 
pictureBox1.Region = new Region(path);

// Method to add the zigzag border to a GraphicsPath object
private void AddZigZagToPath(GraphicsPath path, Rectangle rect, int amplitude, int wavelength)
{
     
    int waves = (int)Math.Ceiling((double)rect.Width / wavelength) + 1;

    // Create an array of points to hold the zigzag points
    PointF[] points = new PointF[waves * 2];

    // Loop through the waves and add the zigzag points
    for (int i = 0; i < waves; i++)
    {
        points[i * 2] = new PointF(i * wavelength, rect.Height - amplitude);
        points[(i * 2) + 1] = new PointF((i * wavelength) + (wavelength / 2), rect.Height);
    }

     
    path.AddLines(points);
    path.AddLine(points[points.Length - 1], new PointF(rect.Width, rect.Height - amplitude));
    path.AddLine(new PointF(rect.Width, rect.Height - amplitude), new PointF(rect.Width, 0));
    path.AddLine(new PointF(rect.Width, 0), new PointF(0, 0));
    path.AddLine(new PointF(0, 0), points[0]);
}