How to set or change Desktop background in C# windows Application

actualy did somthing but that's not working properly, when i changed the image my desktop screen become blue screen nothing else and i already searched on google but i don't got same code:


using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;
using System.IO;
namespace WindowsFormsApplication1
{
public partial class Form2 : Form
{
public Form2()
{
InitializeComponent();
}
[DllImport("user32.dll")]
private static extern bool SystemParametersInfo(uint uiAction, uint uiParam, string pvParam, uint fWinIni);
const uint SPI_SETDESKWALLPAPER = 0x14;
const uint SPIF_UPDATEINIFILE = 0x01;
private void Form2_Load(object sender, EventArgs e)
{

}
public void SetDWallpaper(string path)
{
//SystemParametersInfo(SPI_SETDESKWALLPAPER, 0, path, SPIF_UPDATEINIFILE);
SystemParametersInfo(SPI_SETDESKWALLPAPER, 0, path, SPIF_UPDATEINIFILE);
}
//private void btnset_Click(object sender, EventArgs e)
//{
// SetDWallpaper(fname);
//}
string fname = "";

private void button1_Click(object sender, EventArgs e)
{
OpenFileDialog obj = new OpenFileDialog();
if (obj.ShowDialog() == DialogResult.OK)
{
pictureBox1.Image = Image.FromFile(obj.FileName);
fname = obj.FileName;
}
}

private void button2_Click(object sender, EventArgs e)
{
SetDWallpaper(fname);
}

private void pictureBox1_Click(object sender, EventArgs e)
{

}

}
}



kindly help me it's urgent