(new-object System.Net.WebClient).DownloadFile('https://i.pinimg.com/originals/a1/02/b7/a102b769db321b3ca309f7f9100e8001.jpg',"$Env:Temp\\b.jpg");
Add-Type @"
using System;
using System.Runtime.InteropServices;
using Microsoft.Win32;
namespace Wallpaper
{
 public enum Style : int
{
    Tile, Center, Stretch, NoChange
 }
 public class Setter {
  public const int SetDesktopWallpaper = 20;
  public const int UpdateIniFile = 0x01;
  public const int SendWinIniChange = 0x02;
  [DllImport("user32.dll", SetLastError = true, CharSet = CharSet.Auto)]
  private static extern int SystemParametersInfo (int uAction, int uParam, string lpvParam, int fuWinIni);
  public static void SetWallpaper ( string path, Wallpaper.Style style ) {
     SystemParametersInfo( SetDesktopWallpaper, 0, path, UpdateIniFile | SendWinIniChange );
     RegistryKey key = Registry.CurrentUser.OpenSubKey("Control Panel\\\\Desktop", true);
     switch( style )
     {
        case Style.Stretch :
           key.SetValue(@"WallpaperStyle", "2") ;
           key.SetValue(@"TileWallpaper", "0") ;
           break;
        case Style.Center :
           key.SetValue(@"WallpaperStyle", "1") ;
           key.SetValue(@"TileWallpaper", "0") ;
           break;
        case Style.Tile :
           key.SetValue(@"WallpaperStyle", "1") ;
           key.SetValue(@"TileWallpaper", "1") ;
           break;
        case Style.NoChange :
           break;

     key.Close();
      }
    }
}
"@
[Wallpaper.Setter]::SetWallpaper("$Env:Temp\b.jpg" , 2 )