Set a fake wallpaper when user has no permission to set windows wallpaper

FakeWallpaper.cs

using System;
using System.Drawing;
using System.Windows.Forms;
using System.Runtime.InteropServices;


// Copile with:
// C:\Windows\Microsoft.NET\Framework\v4.0.30319\csc.exe /target:winexe FakeWallpaper.cs

// Compilar with icon file:
// C:\Windows\Microsoft.NET\Framework\v4.0.30319\csc.exe /target:winexe /win32icon:FakeWallpaper.ico FakeWallpaper.cs


public class FakeWallpaper : Form {
    private NotifyIcon notifyIcon;
    private ContextMenuStrip contextMenuStrip;

    [STAThread]
    public static void Main(string[] args) {
        Application.Run(new FakeWallpaper());
    }

    public FakeWallpaper() {
        InitializeComponent();
        this.Load += FakeWallpaper_Load;
    }

    private void InitializeComponent() {
        ToolStripMenuItem closeMenuItem = new ToolStripMenuItem("Close");
        closeMenuItem.Click += (sender, e) => Application.Exit();
        contextMenuStrip = new ContextMenuStrip();
        contextMenuStrip.Items.Add(closeMenuItem);
        notifyIcon = new NotifyIcon() {
            Icon = SystemIcons.Application,
            Visible = true,
            Text = "Fake Wallpaper",
            ContextMenuStrip = contextMenuStrip
        };
    }

    private void FakeWallpaper_Load(object sender, EventArgs e) {
        OpenFileDialog openFileDialog = new OpenFileDialog();
        openFileDialog.Filter = "Imagens|*.jpg;*.jpeg;*.png;*.bmp";

        if (openFileDialog.ShowDialog() != DialogResult.OK) {
            Close();
            return;
        }
        this.BackgroundImage = Image.FromFile(openFileDialog.FileName);
        this.BackgroundImageLayout = ImageLayout.Stretch;
        this.FormBorderStyle = FormBorderStyle.None;
        Rectangle screen = Screen.PrimaryScreen.WorkingArea;
        this.Bounds = screen;
        // "Progman" == Desktop
        IntPtr progman = FindWindow("Progman", null);
        // Cria uma nova janela de WorkerW atrás dos ícones da área de trabalho
        IntPtr result = IntPtr.Zero;
        SendMessageTimeout(progman, 0x052C, new IntPtr(0), IntPtr.Zero, SendMessageTimeoutFlags.SMTO_NORMAL, 1000, out result);
        // Obtém a nova janela de WorkerW
        IntPtr workerw = IntPtr.Zero;
        EnumWindows(new EnumWindowsProc((tophandle, topparamhandle) => {
            IntPtr p = FindWindowEx(tophandle, IntPtr.Zero, "SHELLDLL_DefView", IntPtr.Zero);
            if (p != IntPtr.Zero) {
                workerw = FindWindowEx(IntPtr.Zero, tophandle, "WorkerW", IntPtr.Zero);
            }
            return true;
        }), IntPtr.Zero);
        // Posiciona o formulário abaixo dos ícones da área de trabalho e acima do wallpaper
        SetParent(this.Handle, workerw);
    }


    [DllImport("user32.dll")]
    private static extern IntPtr FindWindow(string lpClassName, string lpWindowName);

    [DllImport("user32.dll")]
    static extern IntPtr FindWindowEx(IntPtr parentHandle, IntPtr childAfter, string className, IntPtr windowTitle);

    [DllImport("user32.dll")]
    static extern IntPtr SendMessageTimeout(IntPtr hWnd, uint Msg, IntPtr wParam, IntPtr lParam, SendMessageTimeoutFlags fuFlags, uint uTimeout, out IntPtr lpdwResult);

    [DllImport("user32.dll")]
    private static extern bool EnumWindows(EnumWindowsProc lpEnumFunc, IntPtr lParam);

    [DllImport("user32.dll")]
    private static extern IntPtr SetParent(IntPtr hWndChild, IntPtr hWndNewParent);

    private delegate bool EnumWindowsProc(IntPtr hWnd, IntPtr lParam);

    [Flags]
    private enum SendMessageTimeoutFlags : uint {
        SMTO_NORMAL = 0x0000,
        SMTO_BLOCK = 0x0001,
        SMTO_ABORTIFHUNG = 0x0002,
        SMTO_NOTIMEOUTIFNOTHUNG = 0x0008
    }
}

FakeWallpaper.ps1

# Running with powershell without compiling:

Add-Type `
    -ReferencedAssemblies System.Drawing,System.Windows.Forms,System.Runtime.InteropServices `
    -Path "$PSScriptRoot\FakeWallpaper.cs"

[FakeWallpaper]::Main("")